Update __init__.py

fix the source file read mode issue.
if use 'r' mode, this may raise a `UnicodeDecodeError`.

jedi/api/__init__.py

@@ -105,7 +105,7 @@ def __init__(self, source=None, line=None, column=None, path=None,
 
         if source is None:
             # TODO add a better warning than the traceback!
-            with open(path) as f:
+            with open(path, 'rb') as f:
                 source = f.read()
 
         self._source = common.source_to_unicode(source, encoding)