Update package.json

updated the underscore version number to 1.5.1 (from 1.3.1). Not lifted to most current version because frontend tests broke from 1.5.2 upwards.
Fix position of import/export popup in timeslider
Revert change on position of imp/exp overlay
Replace "-" with "+" in tooltips with keyboard shortcuts

Ctrl-Shift-L seems counter intuitive as you have to press
the keys together.
Merge pull request #2270 from prtksxna/tooltip

Replace "-" with "+" in tooltips with keyboard shortcuts
Use 'evt.shiftKey' instead of matching 'charCodes'

The shortcut wasn't running consistently and was blocking
'Cmd+L' on Chrome 38. Instead of going to the location bar
it would tooggle the list. Strangely, it did not override
'Cmd+N'. Using `evt.shiftKey` instead of matching the `charCode`
to the uppercase letter solves the problem.
Merge pull request #2271 from prtksxna/keyboard-error

Use 'evt.shiftKey' instead of matching 'charCodes'
Update frontend language tests for new keyboard shortcut convention

8af34a2295f2ff85cf0b introduced a failing test frontend test-
https://travis-ci.org/ether/etherpad-lite/builds/37931978

This commit updates both the German and English strings even though
the German locale files haven't been updated yet. The tests will
continue to fail but will stop as soon as translatewiki catches up.
Merge pull request #2272 from prtksxna/lang-tests

Update frontend language tests for new keyboard shortcut convention
Localisation updates from https://translatewiki.net.
Localisation updates from https://translatewiki.net.
chrome browser change wrapping type
Localisation updates from https://translatewiki.net.
Added explicit reference to plugins and themes in readme
changed link wording for readme plugin reference
Fix for MySQL issues

See https://github.com/Pita/ueberDB/issues/63
bump ueber to require working mysql
bump ueberdb again
Bump resolve

Update dep fixes https://github.com/ether/etherpad-lite/issues/2050
Merge pull request #2116 from jdittrich/updateUnderscore

Underscore Version: Update package.json