clang-format.sh only works with shells supporting `[[ ]]` conditionals

[evaleev]

          This syntax, `[[` and `]]`, is a bash-extension and thus the script does not work on Debian/Ubuntu, where `/bin/sh` is symlinked to `dash`.

A solution is to change the shebang to #!/bin/bash, or use [ and ].

Originally posted by @e-kwsm in #284 (comment)

[evaleev]

Thanks, @e-kwsm ... Clearly I relied too much on AI in writing this :) ksh and zsh also support bash syntax, but since bash seems to be universally available hardwiring to bash seems reasonable to me.

[evaleev]

resolved via #311