Fixes parsing error in Test task where .as or .mxml files within a package that starts with "as" or "mxml"

Current code base incorrectly removes the first instance of ".as" or ".mxml" instead of the last one

Example:
myproject/asmallpackage/MyClass.as
  
C:\development\flexworkspaces\GradleizeFlex\src\module_Mapping\build\reports\FlexUnitRunner.mxml(22):  Error: Syntax error: expecting identifier before as.
          import myprojectmallpackage.as;
With the submitted patch, the proper import is generated:
          import myproject.asmallpackage.MyClass