Fix Eclipse and Idea configuration for Gradle 2.0

When using the plugin with Gradle 2.0 the following error message was returned:

**You can't change configuration 'cucumberCompile' because it is already resolved!**

This is due to the following:

**Gradle 2 updated to Groovy 2.3, which no longer supports the use of += for adding a single element to a collection. So instead of scopes.PROVIDED.plus += configurations.provided it's now scopes.PROVIDED.plus += [configurations.provided]. (The other uses of '+=' are OK.)**

This fix stops that error message from being returned and allows the plugin to work with Gradle 2.0