Update minishift to 1.5.0

[brgnepal]

After making all changes to the cask:

• brew cask audit --download {{cask_file}} is error-free.
• brew cask style --fix {{cask_file}} reports no offenses.
• The commit message includes the cask’s name and version.

Additionally, if updating a cask:

• sha256 changed but version stayed the same ([what is this?][version-checksum]).
  I’m providing public confirmation below.

My testing:

# Edit cask file
$ vim minishift.rb

# Install new cask
$ brew cask install minishift.rb
==> Satisfying dependencies
==> Downloading https://github.com/minishift/minishift/releases/download/v1.5.0/minishift-1.5.0-darwin-amd64.tgz
######################################################################## 100.0%
==> Verifying checksum for Cask minishift
==> Installing Cask minishift
==> Linking Binary 'minishift' to '/usr/local/bin/minishift'.
🍺  minishift was successfully installed!

# Check version
$ /usr/local/bin/minishift version
minishift v1.5.0+ae62cf2

# Audit Check
$ brew cask audit minishift.rb --download
==> Downloading https://github.com/minishift/minishift/releases/download/v1.5.0/minishift-1.5.0-darwin-amd64.tgz
Already downloaded: /Users/devtools/Library/Caches/Homebrew/Cask/minishift--1.5.0.tgz
==> Verifying checksum for Cask minishift
audit for minishift: passed

# Style Check
$ brew cask style minishift.rb

1 file inspected, no offenses detected

[commitay]

Thanks for the PR!