check-code: grep's context flags don't need an extra space before number

A bit of useless trivia found while researching this: OpenBSD's grep's -C has a
default value (of 2) and disallows space before the argument (while -A and -B
allow).

contrib/check-code.py

@@ -148,7 +148,7 b' testpats = ['
     (r'\bsed\b.*[^\\]\\n', "don't use 'sed ... \\n', use a \\ and a newline"),
     (r'env.*-u', "don't use 'env -u VAR', use 'unset VAR'"),
     (r'cp.* -r ', "don't use 'cp -r', use 'cp -R'"),
-    (r'grep.* -[ABC] ', "don't use grep's context flags"),
+    (r'grep.* -[ABC]', "don't use grep's context flags"),
   ],
   # warnings
   [