Fix --warn-no-return with unicode docstrings (#2442)

Author: ddfisher

mypy/checker.py

@@ -668,7 +668,7 @@ def is_trivial_body(self, block: Block) -> bool:
 
         # Skip a docstring
         if (isinstance(body[0], ExpressionStmt) and
-                isinstance(body[0].expr, StrExpr)):
+                isinstance(body[0].expr, (StrExpr, UnicodeExpr))):
             body = block.body[1:]
 
         if len(body) == 0:

test-data/unit/check-flags.test

@@ -93,6 +93,9 @@ def i() -> int:
   """with docstring"""
   ...
 def j() -> int:
+  u"""with unicode docstring"""
+  pass
+def k() -> int:
   """docstring only"""
 
 [case testWarnNoReturnWorksWithAlwaysTrue]