FIX critical ressource leak

As refered to on this page: https://doc.rust-lang.org/std/process/struct.Child.html
you need to wait() each child process to make sure the ressources are properly freed.

This was actually causing the program to crash when calling a command containing a pipe
in a loop.

Author: yxdunc

src/lib.rs

@@ -336,6 +336,7 @@ fn run_full_cmd(process: &mut Process, pipe_last: bool) -> Result<(Child, String
                 Stdio::piped()
             })
             .spawn()?;
+        last_proc.wait();
         last_proc = new_proc;
     }