Added compileOnly to "api" dependencies in plugins.

Same as: https://github.com/decebals/pf4j/blob/master/demo/api/pom.xml#L32

demo_gradle/plugins/plugin1/build.gradle

@@ -23,7 +23,7 @@ task plugin(type: Jar) {
 assemble.dependsOn plugin
 
 dependencies {
-  compile project(':api')
+  compileOnly project(':api') // compileOnly important!!! We do not want to put the api into the zip file since the main program has it already!
   compile 'ro.fortsoft.pf4j:pf4j:1.1.1'
   compile 'org.apache.commons:commons-lang3:3.0'
   testCompile group: 'junit', name: 'junit', version: '4.+'

demo_gradle/plugins/plugin2/build.gradle

@@ -23,7 +23,7 @@ task plugin(type: Jar) {
 assemble.dependsOn plugin
 
 dependencies {
-  compile project(':api')
+  compileOnly project(':api') // compileOnly important!!! We do not want to put the api into the zip file since the main program has it already!
   compile 'ro.fortsoft.pf4j:pf4j:1.1.1'
   compile 'org.apache.commons:commons-lang3:3.0'
   testCompile group: 'junit', name: 'junit', version: '4.+'