[tidy] Check llvm-namespace-comment

Ref: http://clang.llvm.org/extra/clang-tidy/checks/llvm-namespace-comment.html

src/mbgl/util/intersection_tests.cpp

@@ -143,5 +143,5 @@ bool multiPolygonIntersectsMultiPolygon(const GeometryCollection& multiPolygonA,
     return false;
 }
 
-}
-}
+} // namespace util
+} // namespace mbgl