Upgrade to Groovy 2.1.9

** Bug
    * [GROOVY-6080] - IncompatibleClassChangeError: the number of constructors during runtime and compile time
    * [GROOVY-6385] - groovy.bat: Can't use question mark in script parameters
    * [GROOVY-6390] - Super constructor calls are made using MOP with @CompileStatic
    * [GROOVY-6400] - Constructor call with @CompileStatic causes ArrayIndexOutOfBoundsException during compilation
    * [GROOVY-6401] - @CompileStatic type inference bug with overridden methods: causes GroovyCastException at runtime
    * [GROOVY-6402] - @CompileStatic causes null-safe operator to call method twice

** Bug
    * [GROOVY-6012] - GroovyScriptEngine uses UTF-8 on initial compilation, system file.encoding on recompilation
    * [GROOVY-6013] - GroovyScriptEngine disregards source encoding set on its CompilerConfiguration
    * [GROOVY-6156] - Grapes/@Grab does not work with JDK8
    * [GROOVY-6196] - groovy compiler throws ArrayIndexOutOfBoundsException when combining @CompileStatic with @ToString/@EqualsAndHashCode with certain property names
    * [GROOVY-6241] - Type inference fails for methods returning generic map types
    * [GROOVY-6257] - groovydoc information loss for enums
    * [GROOVY-6350] - adding two empty lists fails with NPE
    * [GROOVY-6357] - Inner classes in Groovy should have the same access modifiers as in Java
    * [GROOVY-6365] - Closure taking Object[] in @CompileStatic class gets actual parameters wrapped in additional Object[]
    * [GROOVY-6372] - @Immutable fails to recognize non immutable classes
    * [GROOVY-6379] - Wrong example in the api of class Map(dropWhile)
    * [GROOVY-6384] - Change all calls to Class.forName to direct dispatch so that differences around classloading between Groovy and Java are resolved
    * [GROOVY-6386] - groovyc task throws ZipException when it encounters classpath resources that are not jars

** Improvement
    * [GROOVY-3969] - Groovy Console forgets size of input area
    * [GROOVY-6364] - More efficient implementation of thread safety in class ClassLoaderForClassArtifacts
    * [GROOVY-6371] - Documentation for connection parameters in URL.getText() (and related methods) is lacking
    * [GROOVY-6382] - Bintray JCenter added as a first remote resolver in the default Ivy chain