Merge tag 'v2.2.0'

v2.2.0
strongops cmd now uses public json-file-plus

Note that because it uses the public dependency, it no longer needs to
bundle our github fork.
Merge pull request #104 from strongloop/feature/sln-653-public-json-file-plus

strongops cmd now uses public json-file-plus.
Report failure to read a json file

With an invalid package.json, such as an empty one, `slc strongops
--package` was reporting errors such as:

   Error writing to ./package.json: {}

After this change, the error is:

  Error writing to './package.json': read failed (Unexpected end of input)
Merge pull request #103 from strongloop/feature/fix-sln-721

Report failure to read a json file
Co-install supervisor and cluster-control CLIs
Upgrade loopback-workspace dependency to ~2.3.0
Merge pull request #102 from strongloop/feature/supervisor-support

Co-install supervisor and cluster-control CLIs
v2.2.1
Merge branch 'release/2.2.1' into production