Fix path to proton detection

Proton can be installed into one of `LibraryFolders` listed in
`${HOME}/.local/share/Steam/steamapps/libraryfolders.vdf`,
but not in one detected from `STEAM_COMPAT_CLIENT_INSTALL_PATH`
or `STEAM_COMPAT_DATA_PATH`.

Meanwhile full path to `proton` present in `sys.argv[0]`.

protonfixes/util.py

@@ -26,16 +26,8 @@ def protondir():
     """ Returns the path to proton
     """
 
-    try:
-        proton_dir = glob.glob(os.path.join(
-            os.environ['STEAM_COMPAT_CLIENT_INSTALL_PATH'],
-            'steamapps/common/Proton*'))[0]
-        return proton_dir
-    except IndexError:
-        base = '/'.join(env['STEAM_COMPAT_DATA_PATH'].split('/')[:-2])
-        proton_dir = glob.glob(os.path.join(
-            base, 'common/Proton*'))[0]
-        return proton_dir
+    proton_dir = '/'.join(sys.argv[0].split('/')[:-1])
+    return proton_dir
 
 
 def protonprefix():