E306: fix detection inside async def

Author: asottile

pycodestyle.py

@@ -383,7 +383,7 @@ def blank_lines(logical_line, blank_lines, indent_level, line_number,
                 for line in lines[line_number - top_level_lines::-1]:
                     if line.strip() and expand_indent(line) < ancestor_level:
                         ancestor_level = expand_indent(line)
-                        nested = line.lstrip().startswith('def ')
+                        nested = STARTSWITH_DEF_REGEX.match(line.lstrip())
                         if nested or ancestor_level == 0:
                             break
                 if nested:

testsuite/E30.py

@@ -124,6 +124,11 @@ def a():
     x = 1
     def b():
         pass
+#: E306:3:5
+async def a():
+    x = 1
+    def b():
+        pass
 #: E306:3:5 E306:5:9
 def a():
     x = 2