v0.5.1

PowerGraphics v0.5.1

Diff since v0.5.0

Closed issues:

• conflicting device names creates conflicts in fuel_plot (#54)
• Inconsistent results renewable energy (#58)

Merged pull requests:

• fix fuel bar plot ylabel (#59) (@claytonpbarrows)
• addressing dataframse join deprication warning (#60) (@claytonpbarrows)
• Update .travis.yml (#61) (@jd-lara)
• Cb/fix curtail (#62) (@claytonpbarrows)