Fix reading language map for Kotlin dsl (#124)

It still works fine with groovy build script

gradle/stringGenerator.gradle

@@ -2,8 +2,6 @@ import groovy.json.JsonSlurper
 import groovy.xml.MarkupBuilder
 
 task stringGenerator {
-    final Map<String, String> languageMap = android.extensions.findByName("languageMap")
-
     generate(languageMap)
     println("Strings generated!")
 }
@@ -91,4 +89,4 @@ private static String getDefaultLangKey(Map<String, String> sources) {
         throw new IOException("Can't find default language")
     }
 
-}
+}