Fix json and yaml tags

[bufdev]

I would also like to change the tags to be underscore re: uber-go/fx#256

This also adds go 1.8 as a valid lintable go version.

config.go:37: struct field tag `json:"initial",yaml:"initial"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:38: struct field tag `json:"therafter",yaml:"thereafter"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:51: struct field tag `json:"level",yaml:"level"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:54: struct field tag `json:"development",yaml:"development"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:57: struct field tag `json:"disableCaller",yaml:"disableCaller"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:61: struct field tag `json:"disableStacktrace",yaml:"disableStacktrace"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:63: struct field tag `json:"sampling",yaml:"sampling"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:66: struct field tag `json:"encoding",yaml:"encoding"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:69: struct field tag `json:"encoderConfig",yaml:"encoderConfig"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:72: struct field tag `json:"outputPaths",yaml:"outputPaths"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:75: struct field tag `json:"errorOutputPaths",yaml:"errorOutputPaths"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
config.go:77: struct field tag `json:"initialFields",yaml:"initialFields"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:144: struct field tag `json:"messageKey",yaml:"messageKey"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:145: struct field tag `json:"levelKey",yaml:"levelKey"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:146: struct field tag `json:"timeKey",yaml:"timeKey"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:147: struct field tag `json:"nameKey",yaml:"nameKey"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:148: struct field tag `json:"callerKey",yaml:"callerKey"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:149: struct field tag `json:"stacktraceKey",yaml:"stacktraceKey"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:153: struct field tag `json:"levelEncoder",yaml:"levelEncoder"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:154: struct field tag `json:"timeEncoder",yaml:"timeEncoder"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces
zapcore/encoder.go:155: struct field tag `json:"durationEncoder",yaml:"durationEncoder"` not compatible with reflect.StructTag.Get: key:"value" pairs not separated by spaces

[mention-bot]

@peter-edge, thanks for your PR! By analyzing the history of the files in this pull request, we identified @akshayjshah, @billf and @jcorbin to be potential reviewers.

[akshayjshah]

Commented on the linked issue. Thanks for catching this.

I'm going to push a commit to remove linting on Go 1.8 (from this PR) - we can't typically lint on two separate releases, since they occasionally have conflicting rules (e.g., []Foo{Foo{a: 1}} vs []Foo{{a: 1}}. I'll switch linting to Go 1.8 only in your other PR.