1. Update bower2nix version and add new/updated dependencies into
node-packages-generated.nix. This was done manually, with npm2nix
generating the initial set of derivations. In future, it would be
nice to have an automatic process (see #10358, #9332).
2. Add an override to nodePackages.bower2nix wrapping the commands so
that git is on the PATH.
3. Update fetchbower to support new command-line options of bower2nix,
and to allow github URL tag versions.
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