replaced heredoc delimiter

the usage of heredoc syntax in getSync() and getAsync() functions of BlockJsCache class leads to app/cache/dev/classes.php error... "FatalErrorException: Parse: syntax error, unexpected T_ENCAPSED_AND_WHITESPACE, expecting T_STRING or T_VARIABLE or T_NUM_STRING"

problem seem to be, that the line with the closing identifier CONTENT contain other characters in classes cache file.
Merge pull request #167 from simonchrz/2.1

replaced heredoc delimiter