Add architecture ppc64le to travis build

[ddeka2910]

Thank you for the code.
Add support for architecture ppc64le.
Exclude ruby 2.2.6 for ppc64le as it could not found for installation.
This is part of the Ubuntu distribution for ppc64le. This helps us simplify testing later when distributions are re-building and re-releasing. For more info tag @gerrith3

[coveralls]

Coverage remained the same at 89.545% when pulling ec3d4a2 on ddeka2910:master into ee4388b on technicalpickles:master.

[coveralls]

Coverage remained the same at 89.545% when pulling ec3d4a2 on ddeka2910:master into ee4388b on technicalpickles:master.

[coveralls]

Coverage decreased (-0.02%) to 89.522% when pulling ec3d4a2 on ddeka2910:master into ee4388b on technicalpickles:master.