clang-format: Fix incorrect lambda recognition exposed by r203452.

Before:
  int i = a[a][a] -> f();

After:
  int i = a[a][a]->f();

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203556 91177308-0d34-0410-b5e6-96231b3b80d8