Remove inconsequential calls to fetchSession()

[assemblethis]

This is a PR for the issue I raised in #34. In the sync, pull, push, and changes functions, there is a call to fetchSession() that returns a promise but nothing is being done with the returned promise. The fetchSession() method doesn't seem to have any side effects that would be useful after the sync, pull, push, or changes calls on the db. It seems to be inconsequential code, so I suggest removing it with this PR.

[MDSLKTR]

@assemblethis This is looking good and removes some rather useless calls which should make it a bit lighter on the network in general, feel free to merge when you're done. Thanks!

[assemblethis]

Thanks, maybe we should release a version 0.3.5 in a little bit. Let me run this latest through a few more manual tests though.

[assemblethis]

All unit tests passed:

PASS tests/testData.spec.js
Pouch options are returned by function
Unit Tests that todos is defined on Vue components
V Test Plugin with Empty Data Function (15ms)
V Test Plugin with Empty Data Object (11ms)
V Test Plugin with No Data Function Or Object (1ms)
V Test Plugin with Existing Data Function (2ms)
Unit Tests to see that the todos property on the data root level is connecte
d with the todos property on the vue instance (this is what the beforeCreate lif
ecycle hook does)
V Test Plugin with Empty Data Function (2ms)
V Test Plugin with Empty Data Object (1ms)
V Test Plugin with No Data Function Or Object (2ms)
V Test Plugin with Existing Data Function (1ms)
Pouch options are objects
Unit Tests that todos is defined on Vue components
V Test Plugin with Empty Data Function (1ms)
V Test Plugin with Empty Data Object (2ms)
V Test Plugin with No Data Function Or Object (2ms)
V Test Plugin with Existing Data Function (2ms)
Unit Tests to see that the todos property on the data root level is connecte
d with the todos property on the vue instance (this is what the beforeCreate lif
ecycle hook does)
V Test Plugin with Empty Data Function (2ms)
V Test Plugin with Empty Data Object (2ms)
V Test Plugin with No Data Function Or Object (6ms)
V Test Plugin with Existing Data Function (1ms)
Set selector to null
V Test Plugin with Reactive Selector that can return null (2ms)

And manual tests too

[MDSLKTR]

Published to npm as pouch-vue 0.3.5, thanks @assemblethis