Fix for ENOENT

Fixing error "Fatal error: Unable to read "pmd.xml" file (Error code: ENOENT)." on Grunt v0.4.5.
files.js method signature is file.copy = function(srcpath, destpath, options) but in flexpmd.js you are passing grunt.file.copy(dest, outputFile);.
In other words dest and outputFile have to be swapped like this grunt.file.copy(outputFile,dest).