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;
  }

llvm-svn: 193050