Fix erroneous regex repetition.

Author: eddieantonio

pycodestyle.py

@@ -121,7 +121,7 @@
 OPERATOR_REGEX = re.compile(r'(?:[^,\s])(\s*)(?:[-+*/|!<=>%&^]+)(\s*)')
 LAMBDA_REGEX = re.compile(r'\blambda\b')
 HUNK_REGEX = re.compile(r'^@@ -\d+(?:,\d+)? \+(\d+)(?:,(\d+))? @@.*$')
-STARTSWITH_DEF_REGEX = re.compile(r'^(async\b+def|def)')
+STARTSWITH_DEF_REGEX = re.compile(r'^(async\s+def|def)\b')
 STARTSWITH_TOP_LEVEL_REGEX = re.compile(r'^(async\s+def\s+|def\s+|class\s+|@)')
 STARTSWITH_INDENT_STATEMENT_REGEX = re.compile(
     r'^\s*({0})\b'.format('|'.join(s.replace(' ', '\s+') for s in (