Don't use IReadOnlyDictionary because of mono

In mono 4.2, ConcurrentDictionary doesn't implement IReadOnlyDictionary
and so Npgsql bombs.

Fixes npgsql#875

Second beta8 release

The first beta8 release included dependencies from the myget feeds which
weren't available at nuget.org. Removed the myget feeds and rebuilt.

Changes for beta8 release

Removed signing since EF7 itself isn't signed

v2.2.7

Toggle v2.2.7's commit message

Merge branch 'hotfix/2.2.7' into support/2.x