LOAD_ASSERT can also be an expr

This may have the undesirable property that assert statements might get
tagged with equivalant low-level Python code that uses "raise
AssertionError", but so be it.

Fixes #103

uncompyle6/parser.py

@@ -442,6 +442,7 @@ class PythonParser(GenericASTBuilder):
     def p_expr(self, args):
         '''
         expr ::= _mklambda
+        expr ::= LOAD_ASSERT
         expr ::= LOAD_FAST
         expr ::= LOAD_NAME
         expr ::= LOAD_CONST