Fix flowtype errors in babel-plugin-emotion

[bigslycat]

What:

I received this errors using Flow version 0.54.0:

Error: packages/babel-plugin-emotion/src/index.js:121
121:         moduleName = JSON.parse(packageJsonContent).name
                                     ^^^^^^^^^^^^^^^^^^ Buffer. This type is incompatible with the expected param type of
485:     static parse(text: string, reviver?: (key: any, value: any) => any): any;
                            ^^^^^^ string. See lib: /tmp/flow/flowlib_2d62ca57/core.js:485

Error: packages/babel-plugin-emotion/src/parser.js:97
 97: export function parse(css, opts) {
                           ^^^ parameter `css`. Missing annotation

Error: packages/babel-plugin-emotion/src/parser.js:97
 97: export function parse(css, opts) {
                                ^^^^ parameter `opts`. Missing annotation

Why:

If we use Flow, we must not ignore this error reports.

How:

The type of the variable is explicitly converted to string. Function parse in parser.js is annotated.

Checklist:

• Documentation
• Tests
• Code complete

[codecov-io]

Codecov Report

Merging #293 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #293   +/-   ##
=======================================
  Coverage   90.37%   90.37%           
=======================================
  Files          21       21           
  Lines         966      966           
  Branches      260      260           
=======================================
  Hits          873      873           
  Misses         75       75           
  Partials       18       18

Impacted Files	Coverage Δ
packages/babel-plugin-emotion/src/parser.js	95.12% <ø> (ø)	⬆️
packages/babel-plugin-emotion/src/index.js	97.74% <100%> (ø)	⬆️

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[tkh44]

Released in 7.2.2