git "insufficient permission" error when running jspm install

Nobody has claimed this yet.

I've been using jspm-cli for quite some now, and JUST after bootstrapping the dotfiles with the default .gitconfig settings, I've begun receiving the following error with every `jspm install` command:

```
warn Error on getOverride for jspm:npm, retrying (1).
Error: Command failed: /bin/sh -c git fetch --all && git reset --hard origin/master
error: insufficient permission for adding an object to repository database .git/objects
fatal: failed to write object
fatal: unpack-objects failed
error: Could not fetch origin

at ChildProcess.exithandler (child_process.js:751:12)
at ChildProcess.emit (events.js:110:17)
at maybeClose (child_process.js:1015:16)
at Socket. (child_process.js:1183:11)
at Socket.emit (events.js:107:17)
at Pipe.close (net.js:485:12)
```

I'm curious if anyone can spot where the dotfiles might have affected my git permissions in such a way that jspm starts complaining -- particularly when it attempts a `/bin/sh -c git fetch --all && git reset --hard origin/master` command.

It might be worth noting that I currently have my versions of npm and node managed through nvm, and both of those still work as expected (as does git itself).

Start by reviewing the default .gitconfig settings involved in the dotfiles bootstrap, then reproduce jspm install and the shown `git fetch --all && git reset --hard origin/master` command. Check whether the repository’s `.git/objects` permissions are affected; done means identifying the responsible dotfiles setting or documenting that the failure is external to this repository.

Written by the indexing model from the issue text.