Fixes #77
Fixes #77

Now mongo hacker fails if ~/.mongorc.js already exists. This is
a more safe behavior for those who may accidentally override their
existing ~/.mongorc.js files without realizing.

stennie/mongo-hacker,tjjalava/mongo-hacker,hhzplst/mongo-hacker,hristozov/mongo-hacker,bradparks/mongo-hacker,Cog-g/mongo-hacker,pvdb/mongo-hacker,vaelen/mongo-hacker,digitalartcrew/mongo-hacker,TylerBrock/mongo-hacker,vorou/mongo-hacker,AustenLR/mongo-hacker