Gradle sample on travis (#3114)

* Explicitly ignore .bak in gradle samples directory

* Add gradle wrapper to local-spec sample, make .java-version (jenv local) be less machine specific

* Include gradle plugin samples in travis build

Author: jimschubert

.java-version

@@ -1 +1 @@
-oracle64-1.8.0.152
+1.8

.travis.yml

@@ -134,6 +134,9 @@ script:
   # test maven plugin
   - mvn clean compile -f modules/openapi-generator-maven-plugin/examples/java-client.xml
   - mvn clean compile -f modules/openapi-generator-maven-plugin/examples/multi-module/pom.xml
+  # test gradle plugin
+  - (cd modules/openapi-generator-gradle-plugin/samples/local-spec && ./gradlew buildGoSdk)
+  - (cd modules/openapi-generator-gradle-plugin/samples/local-spec && ./gradlew openApiGenerate)
 after_success:
   # push to maven repo
   - if [ $SONATYPE_USERNAME ] && [ "$TRAVIS_PULL_REQUEST" == "false" ]; then

modules/openapi-generator-gradle-plugin/samples/.gitignore

@@ -0,0 +1 @@
+.bak/

modules/openapi-generator-gradle-plugin/samples/local-spec/gradle/wrapper/gradle-wrapper.jar

@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.10.2-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists