Use unicode() instead of str() on Python 2

Tag: v1.13+jsondiff.0

Merge tag 'v1.13' into v1.13+jsondiff

Tag: v1.12+jsondiff.0

Merge tag 'v1.12' into v1.12+jsondiff

Tag: v1.11+jsondiff.0

Merge tag 'v1.11' into v1.11+jsondiff

Tag: v1.9+jsondiff.1

Tag: v1.9+jsondiff.0

release v1.13

release v1.12

release v1.11

release v1.10