Upgrade lunr.js from 0.4.3 to  0.5.2

https://github.com/olivernn/lunr.js/blob/master/CHANGELOG.mdown
Changelog
0.5.2

Use npm they said, it'll be easy they said.
0.5.1

Because npm issues :(
0.5.0

Add plugin support to enable i18n and other extensions to lunr.
Add AMD support #72 thanks lnwdr.
lunr.Vector now implemented using linked lists for better performance especially in indexes with large numbers of unique tokens.
Build system clean up.
0.4.5

Fix performance regression introduced in 0.4.4 by fixing #64.
0.4.4

Fix bug #64 idf cache should handle tokens with the same name as object properties, thanks gitgrimbo.
Intersperse source files with a semicolon as part of the build process, fixes #61, thanks shyndman.
Merge pull request #1 from vivekkiran/patch-1

Upgrade lunr.js from 0.4.3 to  0.5.2