Updating levelup dependency

[pzagor2]

This PR updateds levelup to the latest version. The need for this update was discussed in this issue for ethereumjs-client project.

I ran the tests and they are all passing.
I ran the example code on my Geth DB, it seems to run OK.

[coveralls]

Coverage decreased (-0.004%) to 97.934% when pulling ade93e5 on pzagor2:updading-levelup into a0581ef on ethereumjs:master.

[holgerd77]

Hi @pzagor2, these commit messages are a super-mess 😄, can you please clean them up into one commit with a proper commit message on it? Otherwise thanks for the PR, very appreciated! Cool, that you manually tested the example as well!

[vpulim]

Hi @pzagor2, these commit messages are a super-mess 😄, can you please clean them up into one commit with a proper commit message on it? Otherwise thanks for the PR, very appreciated! Cool, that you manually tested the example as well!

@pzagor2 The easiest way to combine these into one commit is like this:

git checkout updading-levelup
git reset --soft master
git commit -am 'Update levelup dependency'
git push --force origin updading-levelup

[pzagor2]

Thank you for the comments.

I pushed the fixes with cleaned up commit history.
@vpulim Let me know if there is anything else I need to add or update.

[vpulim]

@pzagor2 Changes look good to me. The Travis build is failing however with a strange error message about a missing ‘./clone.js’ file. I’ll take a look as well... it could just be a bug with Travis

[vpulim]

Ok, I re-ran the travis build and it worked the second time (annoying). @holgerd77 Are you ok with loosening the coverage requirements slightly so this PR passes? The code changes didn't add any new lines of code... the coverage decreased only because the new code was shorter in length.

[holgerd77]

@vpulim We already started at some point to add coverage decrease thresholds for the various libraries because that's always some point of pain. I added a decrease threshold of 0.5% now and an absolute threshold of 95%.

[holgerd77]

Looks good, see comments from @vpulim.

[holgerd77]

Ok, just tested, with a review this is mergeable (not sure, maybe this was already be the case before as well, just a red x on the check not necessarily means a block for merging, in the case that the check itself is not set to be mandatory).

[holgerd77]

(@vpulim: will leave this open for merge nevertheless, think you are more into the leveldb update topic right now.)

[vpulim]

@holgerd77 Thanks. Merging now.
@pzagor2 Thanks for this PR!