Fix missing comma in .clang-tidy config.

`clang-tidy --dump-config` shows that it had trouble around
that line and the next and thus was not properly processing these.

Signed-off-by: Henner Zeller <h.zeller@acm.org>

Author: hzeller

.clang-tidy

@@ -8,7 +8,7 @@ Checks: >
   -clang-analyzer-cplusplus.NewDeleteLeaks,
   -clang-analyzer-optin.performance.Padding,
   readability-*,
-  -readability-identifier-naming
+  -readability-identifier-naming,
   -readability-braces-around-statements,
   -readability-convert-member-functions-to-static,
   -readability-function-cognitive-complexity,