CPPKAFKA_VERSION_MINOR Not Updated

[rriggs]

I noticed the warning in the release notes for 0.3.0 that the ABI changed. I would expect that the SONAME changes when the ABI changes. Was this an oversight? It seems a bump to CPPKAFKA_VERSION_MINOR is warranted when the ABI changes.

[mfontanini]

This was a (very bad) oversight on my side. I don't like altering history but I'll probably go back and re-tag 0.3.0 and 0.3.1 so they have the right soname.