automated upload to OSS repos

A v0.4 release has been pushed to oss.sonatype.org but is not yet synch-ed with Maven Central. I will then be able to test how to consume the plugin and document it. Most likely, it will look like this.

```groovy
apply plugin: 'cucumber'                                                                            
                                                                                                    
buildscript {                                                                                       
    repositories {                                                                                  
        mavenCentral()                                                                              
    }                                                                                               
                                                                                                    
    dependencies {                                                                                  
        classpath 'com.github.samueltbrown:gradle-cucumber-plugin:0.4'                              
    }                                                                                               
}                                                                                                   
```