fix(mobile): resolve push hanging

[ras0q]

ref: #609 #574

async push() for mobile is implemented using this.branchInfo(), but this branch info should be converted to latest commit hash.

[Vinzent03]

Did you encounter one of these two branches being null? I'm pretty sure the ref for a Tree can also just be the branch name.

[ras0q]

I don't encounter that and using both the branch name and the commit hash can be the ref for a tree.
However by using the commit hash, I think git.TREE({ ref }) can be resolved more quickly.
https://github.com/isomorphic-git/isomorphic-git/blob/53310498e9dd84a213197de2d69047ce733580e6/src/managers/GitRefManager.js#L193

[ras0q]

Here is my brief benchmark!
https://github.com/ras0q/isomorphic-git-walk-test

[ras0q]

@denolehov @Vinzent03 could you review this PR? Thanks!

[antgiant]

Adding #653 as another instance.

I’m experiencing this too

[Vinzent03]

When digging the code of TREE() it uses `resolveRef()', just like you do now manually. I don't see what this pr actually changes.