Test on CircleCI

More closely match MIT License text verbatim

Tweak the license such that tooling (in particular, `licensee`) recognizes the LICENSE file as MIT.

Before:

```
$ /usr/local/share/gem/bin/licensee 
License:        NOASSERTION
Matched files:  LICENSE, README.markdown, method_source.gemspec
LICENSE:
  Content hash:  bfd1a6d003c3210704bb2025ee95bfc059adcd4d
  License:       NOASSERTION
README.markdown:
  Content hash:  d64f3bb4282a97b37454b5bb96a8a264a3363dc3
  Attribution:   Copyright (c) 2011 John Mair (banisterfiend)
  Confidence:    100.00%
  Matcher:       Licensee::Matchers::Exact
  License:       MIT
method_source.gemspec:
  Confidence:  90.00%
  Matcher:     Licensee::Matchers::Gemspec
  License:     MIT
```

After:
```
$ /usr/local/share/gem/bin/licensee 
License:        MIT
Matched files:  LICENSE, README.markdown, method_source.gemspec
LICENSE:
  Content hash:  d64f3bb4282a97b37454b5bb96a8a264a3363dc3
  Attribution:   Copyright (c) 2011 John Mair (banisterfiend)
  Confidence:    100.00%
  Matcher:       Licensee::Matchers::Exact
  License:       MIT
```

Handle new message for unterminated lists on MRI 2.7

The error message for `issue = %W/` changed, before:

```
(eval):2: syntax error, unexpected tSTRING_END, expecting tSTRING_CONTENT or tSTRING_DBEG or tSTRING_DVAR or ' '
```

After:

```
((eval):2: unterminated list meets end of file)
```

Fix CI builds and add newer ruby versions