Fix NPM loose comparisons

[kmck]

Hey, thanks for this library!

I noticed that loose requirements weren't evaluating as expected for NPM. It seems like this is because null minor/patch versions default to zero, but I believe the correct behavior is to stop comparison at any missing parts of the semver.

For example, "2.0.2" satisfies "=2" is more like "2 satisfies "=2" than "2.0.2" satisfies "=2.0.0", if that makes sense.

I changed isGreaterThan and isEqualTo when type is SemverType.NPM so that it more closely matches the behavior in Node. I had to fix one erroneous test that asserted that new Semver("2.0.1", SemverType.NPM).satisfies(">2.0 <3.0") should be true (it should ignore the patch version because the requirement isn't fully qualified). All the rest were fine. I added a couple more tests for good measure.

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Update:

I tried to add a few more test cases and noticed that they failed. After digging in a little, it looks like the implementation of toReversePolishNotation was a little off.

Everything is supposed to get added to one side of the queue, but apparently some tokens were getting added to the other side instead, perhaps to make unary operators work. I think the trick for unary operators is not to add the two tokens to the front of the queue, but to add them in the back in reverse order.

I flipped req1 and req2 in evaluateReversePolishNotation to keep the tests happy, but the way it evaluates is still equivalent (woo commutative property).

I believe these changes address the unexpected behavior mentioned in #15 and #29

[vdurmont]

Looks perfect! Thanks for this super high quality PR! I'll merge and release a new version soon with those changes.

[vdurmont]

@kmck v3.1.0 is now available on Maven Central and includes your fix.

[kmck]

Cool, thanks for the fast release!