clang-format: Support case ranges.

Before (note the missing space before "..." which can lead to compile
errors):
  switch (x) {
    case 'A'... 'Z':
    case 1... 5:
        break;
  }

After:
  switch (x) {
    case 'A' ... 'Z':
    case 1 ... 5:
        break;
  }

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193050 91177308-0d34-0410-b5e6-96231b3b80d8