Fix issue with missing version in dependency

* that could provoke issues with projects including cf-env with the error `'dependencies.dependency.version' for org.springframework.boot:spring-boot-starter-test:jar is missing. in io.pivotal.cfenv:java-cfenv:3.1.0`
`

Author: anthonydahanne

java-cfenv/build.gradle

@@ -17,7 +17,7 @@ dependencies {
     }
 
     testFixturesApi platform("org.springframework.boot:spring-boot-dependencies:${springBootVersion}")
-    testFixturesImplementation "org.springframework.boot:spring-boot-starter-test"
+    testFixturesImplementation "org.springframework.boot:spring-boot-starter-test:${springBootVersion}"
     testFixturesImplementation "org.jmockit:jmockit:${jmockitVersion}"
 }