Updates curb to v0.8.6
Updates curb to v0.8.6

This adds compatibility for ruby 2.2.0 while retaining compatibility
with 2.0.x and 2.1.x.

More info: https://github.com/taf2/curb/pull/197

adscott/stringer,dandorman/stringer,run-project/stringer,thiagosil/stringer,jqr/stringer,thiagosil/stringer,nibble/stringer,milligramme/stringer,run-project/stringer,swanson/stringer,InPermutation/stringer,nobuti/stringer,nobuti/stringer,Koronen/stringer,geemus/stringer,geemus/stringer,swanson/stringer,adscott/stringer,mpraglowski/stringer,nibble/stringer,swanson/stringer,swanson/stringer,nibble/stringer,mpraglowski/stringer,milligramme/stringer,lodestone/stringer,dandorman/stringer,Koronen/stringer,milligramme/stringer,jqr/stringer,geemus/stringer,jeroenj/stringer,jeroenj/stringer,dperson/stringer,geemus/stringer,dperson/stringer,Koronen/stringer,InPermutation/stringer,thiagosil/stringer,run-project/stringer,nobuti/stringer,nibble/stringer,jqr/stringer,dperson/stringer,Koronen/stringer,lodestone/stringer,dperson/stringer,InPermutation/stringer,jeroenj/stringer,jeroenj/stringer,adscott/stringer,jqr/stringer,adscott/stringer,dandorman/stringer,mpraglowski/stringer,lodestone/stringer