Dont raise if rubygem is nil on dependency

[fixes #653]
Merge pull request #688 from arthurnn/try_rubygem_name

Dont raise if rubygem is nil on dependency
Update newrelic_rpm to version 3.8.1.221
Update dalli to version 2.7.2
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Merge pull request #689 from skottler/deploy_linkto_commit

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Update code to work with rubygems 2.2.2+
Optimize load_spec
Run travis on multiple rubyversions
Replace format with package