Fixed stemming words ending with letter 'y' according to Porter2 algorithm

[MihaiValentin]

While searching for the word lay, I noticed that there are no results, though I had a lot of layout words in my documents.

When debugging, I noticed that lay was transformed into lai, due to step 1c from the Porter2 algorithm.

When reviewing step 1c, I noticed that we should only convert the y to i in words containing non-vowels before y, so lay should have stayed lay after this step.

This PR contains the correct implementation of step 1c. I've also added two test fixtures.

[jure]

:+1:

https://github.com/mdirolf/pyporter2/blob/master/Stemmer.py#L135-L140

https://github.com/nemec/porter2-stemmer/blob/master/Porter2Stemmer.UnitTest/EnglishPorter2StemmerUnitTest.cs#L749-L790

https://github.com/kristopolous/Porter2-Stemmer/blob/master/validate_PorterStemmer2/ReferenceTable.js#L26865

https://github.com/kristopolous/Porter2-Stemmer/blob/master/validate_PorterStemmer2/ReferenceTable.js#L14943

[olivernn]

Good spot, thanks for providing a fix!

Before I merge this please could you remove the build artefacts from the commit (lunr.js and lunr.min.js).

[MihaiValentin]

I removed the build artifacts.

[olivernn]

I've just pushed 0.5.3 which includes your fix for this bug, thanks!