ammonite-repl: Add shebang to amm executable

[mdedetrich]

New versions of the ammonite-repl don't include the shebag inside the executable which means it fails to execute if you aren't in a Bourne compliant shell (such as fish)

This fixes com-lihaoyi/Ammonite#813

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[ilovezfs]

This is an upstream issue. We shouldn't need to prepend shebang lines.

[ilovezfs]

Thanks for the PR nonetheless @mdedetrich!

[mdedetrich]

@ilovezfs Incase it takes upstream for a while, is it possible to fix the formula for the current release (and if so, is this something that is done using patch or is the approach used in this PR acceptable?)

[ilovezfs]

@mdedetrich let's see what upstream says first.

[mdedetrich]

@ilovezfs Upstream commented, basically it will take a while to post a fix (the reason why the script doesn't have the shebang in there is because it was universally for both *nix/MacOSX and Windows). I am going to do a PR to fix the changes but its not trivial (I am also on vacation currently).

I am not sure what the rules are in regards to temporary fixes, note that this PR is meant to idempotent (i.e. it will only add the shebang if it doesn't exist), so if it gets fixed at some point in the future nothing will break.

There is also an argument from upstream that this is the responsibility of the OS installing the library rather than the release of the library itself (in the same way that we have the chmod files, which is perfectly acceptable)