[pig] $ sign can conflict as a parameter in regexps

Very similar to HUE-1958, we should probably not match $ when it as a \ before

http://stackoverflow.com/questions/27042742/end-of-line-anchor-throwing-error-in-hue-pig-editor

REGEX_EXTRACT(cs, '((;|^)u=(.*?)([^0-9a-z-A-Z]|
$))', 3)