Do not wait for a parallel process to finish

@dankocherga, for me it seems the module doesn't actually work withouth
this commmit.

According to php.net documentation:

   If a program is started with this function, in order for it to
   continue running in the background, the output of the program must be
   redirected to a file or another output stream. Failing to do so will
   cause PHP to hang until the execution of the program ends.
Refactor test
Merge pull request #8 from vsushkov/fix-hanging

Do not wait for a parallel process to finish