Various HELM_VERSION in Dockerfile.*

[vochicong]

Why different HELM_VERSION in Dockerfile.*

$ grep "ENV HELM_VERSION" Dockerfile*
Dockerfile.common:ENV HELM_VERSION 2.10.0-rc.1
Dockerfile.php:ENV HELM_VERSION 2.8.2
Dockerfile.ruby:ENV HELM_VERSION 2.8.2
Dockerfile.slim:ENV HELM_VERSION 2.9.1
Dockerfile.swift:ENV HELM_VERSION 2.8.2

It seems causing the problem at
jenkins-x/jx#1419

[jglick]

#653 updated one of them.