fix: syntax error in ghciwatch command causing ghciwatch to error out when multiple hs files are in the app folder

[mtamc]

--watch app/*.hs gets expanded to --watch app/File1.hs app/File2.hs which is unsupported and causes the following error:

ghciwatch --after-startup-ghci :main --after-reload-ghci :main --watch app/*.hs --debounce 50ms --command 'wasm32-wasi-cabal repl app -finteractive --repl-options="-fghci-browser -fghci-browser-port=8080"'
error: the argument '[FILE]' cannot be used with '--command <SHELL_COMMAND>'

Usage: ghciwatch [--command SHELL_COMMAND] [--watch PATH] [OPTIONS ...]

For more information, try '--help'.
make: *** [Makefile:18: watch] Error 2

According to the docs the correct syntax is --watch app or --watch app/File1.hs --watch app/File2.hs. https://mercurytechnologies.github.io/ghciwatch/cli.html#--watch

This PR simply uses --watch app.