Promotion with release specified assumes the first matching appname is the one to be promoted

[tomhobson]

In an example where I have the helmfile (with unnecessary fields removed)

releases:
- chart: dev/myapp
  name: myapp
- chart: dev/myapp
  name: myapp-beta

And I promote like so
jx promote --release myapp-beta with the version 1.0.0

The helmfile will be wrongly edited so the resulting helmfile would look like so

releases:
- chart: dev/myapp
  name: myapp
  version: 1.0.0
- chart: dev/myapp
  name: myapp-beta

The correct helmfile should look like

releases:
- chart: dev/myapp
  name: myapp
- chart: dev/myapp
  name: myapp-beta
  version: 1.0.0

Pullable PR to play around with (if you require it)
#388