Update Jenkins button styles

Uses the same styles as in #1279. 

<img src="https://camo.githubusercontent.com/03a8a4f641dcbbf613f2e573b5f2023bae4de7c0/68747470733a2f2f6170692e6d6f6e6f736e61702e636f6d2f696d6167652f646f776e6c6f61643f69643d46596b7876354b7a6d62744e676775434e436473324a5430654a646a496a" />

Before:

<img src="https://api.monosnap.com/image/download?id=zYIJaeC5RD1NXQumPlpN8YdGVHct4Z" />

After:

<img src="https://api.monosnap.com/image/download?id=gr43K5pNaQwIFWElM46Dik6G538Oks" />