docs: Update Groovy project url (#63)

docs: Update Groovy project url

docs/guide/src/docs/asciidoc/groovy.adoc

@@ -1,7 +1,7 @@
 [[_groovy]]
 = Using Json-lib with Groovy
 
-Since version 2.0 Json-lib has integrated http://groovy.codehaus.org[Groovy]
+Since version 2.0 Json-lib has integrated https://groovy-lang.org/[Groovy]
 support, meaning that POGOs can be transformed into JSON and back,
 in the same manner as you do now with POJOs. There are other features as well:
 
@@ -40,4 +40,4 @@ def strAsFunc = "function(param){ this.param = param; }" as JSONFunction
 
 WARNING: Since version 2.2.1 Json-lib will not automatically enhance class through
          custom metaclasses, you must call GJson.enhanceClasses() before executing
-         the examples shown on this page.
+         the examples shown on this page.