Rely on the user to provide a jcenter-compatible repository by default

Fixes #18

src/integTest/groovy/com/github/jrubygradle/storm/JRubyStormTaskIntegrationSpec.groovy

@@ -39,6 +39,11 @@ buildscript {
 }
 apply plugin: 'com.github.jruby-gradle.storm'
 
+repositories {
+    jcenter()
+    mavenLocal()
+}
+
 jrubyStorm {
 }
     """

src/main/groovy/com/github/jrubygradle/storm/JRubyStormPlugin.groovy

@@ -21,8 +21,6 @@ class JRubyStormPlugin implements Plugin<Project> {
     @PackageScope
     void updateRepositories(Project project) {
       project.repositories {
-        // jcenter contains the redstorm and gradle dependencies
-        jcenter()
         // Repositories for Storm dependencies
         maven { url 'http://clojars.org/repo/' }
         maven { url 'http://conjars.org/repo/' }