Moved variable with script path out of function

Otherwise it will point to the current path, instead of script path.
Changing it to script variables will change that behaviour to desirable one.

plugin/pythonhelper.vim

@@ -1,8 +1,8 @@
 " File: pythonhelper.vim
 " Author: Michal Vitecek <fuf-at-mageo-dot-cz>
 " Author: Roman Dobosz <gryf@vimja.com>
-" Version: 0.84
-" Last Modified: 2016-05-21
+" Version: 0.85
+" Last Modified: 2016-05-24
 "
 " Overview
 " --------
@@ -33,15 +33,16 @@
 
 " VIM functions {{{
 let g:pythonhelper_python = 'python'
+let s:plugin_path = expand('<sfile>:p:h', 1)
+
 function! s:PHLoader()
-    let l:plugin_path = escape(expand('<sfile>:p:h'), '\')
 
     if !exists('g:pythonhelper_py_loaded')
         if has('python')
-            exe 'pyfile ' . escape(l:plugin_path, ' ') . '/pythonhelper.py'
+            exe 'pyfile ' . s:plugin_path . '/pythonhelper.py'
         elseif has('python3')
             let g:pythonhelper_python = 'python3'
-            exe 'py3file ' . escape(l:plugin_path, ' ') . '/pythonhelper.py'
+            exe 'py3file ' . s:plugin_path . '/pythonhelper.py'
         else
             echohl WarningMsg|echomsg
                         \ "PythonHelper unavailable: "