Move node-zip require inside war task config

Node-zip required once outside of the task configuration causes node-zip
to add all previous source files to all future WAR's. Creating multiple
WAR's with different source files included causes all previously
included files to be added to the currently generated WAR.
Increment version to 0.2.7 and update README
Merge pull request #4 from jbenner/master

Move node-zip require inside war task config