Use helm 2.14.3 for now

Helm 2.15.0 broke for us (#338 (closed)), and helm 2.15.1 might be responsible for #357 (closed). We need to upgrade a few components but for the upcoming OAS 0.2.1 release we stay with helm 2.14.3.

This reverts commit ae877752, reversing changes made to cd1ad365.