exceptions.rb: move alternative solution to a new line

[maxim-belkin]

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The message that Homebrew spits out when build tools are not available is not formatted appropriately:

Error: The following flag:
  --build-from-source
requires building tools, but none are installed.
Install Clang or brew install gccAlternatively, remove the flag to attempt bottle installation.
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:79:in `prevent_build_flags'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:119:in `install'
/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/brew.rb:105:in `<main>'

This PR adds a new line before Alternatively, ....

[MikeMcQuaid]

@maxim-belkin Just remove both the chomps?

[maxim-belkin]

That would work too

[MikeMcQuaid]

Thanks @maxim-belkin!