Fix exceptions caused by blob.content including `\n`
Fix exceptions caused by blob.content including `\n`

octotree stopped in some repositories.
e.g.: https://github.com/ReactiveCocoa/ReactiveCocoa

Some blob returns base64 content including `\n`.
This cause exception in `atob()` and stop octotree.
The document does not mention about it.
https://developer.github.com/v3/git/blobs/#get-a-blob

Ephemera/octotree,codevlabs/octotree,SampleLiao/octotree,hexing-w/octotree,nntoan/octotree,ldnguyen58/octotree,mdibaiee/octotree,tamdao/octotree,kidaa/octotree,mikestaub/octotree,likaiwalkman/octotree,Brightcells/octotree,shiningguang/octotree,likaiwalkman/octotree,JimiHFord/octotree,ahlfors/octotree,zhutaorun/octotree,duylam/octotree,jamez14/octotree,zhutaorun/octotree,buunguyen/octotree,jamez14/octotree,buunguyen/octotree,tamdao/octotree,Brightcells/octotree,guidiego/octotree,nntoan/octotree,Havi4/octotree,mikestaub/octotree,crashbell/octotree,FroggyStyle/octotree,treejames/octotree,FroggyStyle/octotree,ahlfors/octotree,Ephemera/octotree,guidiego/octotree,codevlabs/octotree,tsdl2013/octotree,treejames/octotree,christer155/octotree,tsdl2013/octotree,ldnguyen58/octotree,JimiHFord/octotree,christer155/octotree,shiningguang/octotree,duylam/octotree,kidaa/octotree,mdibaiee/octotree,hexing-w/octotree,SampleLiao/octotree,Havi4/octotree,crashbell/octotree