Adhere to new standards: don't alter const variables
Adhere to new standards: don't alter const variables

This was causing muttator not to work with Thunderbird 36 anymore.

nullren/vimperator-labs,Quicksaver/vimperator-labs,Sheile/vimperator-labs,nullren/vimperator-labs,zklinger/vimperator-labs,Quicksaver/vimperator-labs,Sheile/vimperator-labs,airodactyl/airodactyl,Evidlo/vimperator-labs,derenio/vimperator-labs,zklinger/vimperator-labs,paretje/vimperator-labs,Evidlo/vimperator-labs,seanmorton/vimperator-labs,seanmorton/vimperator-labs,stemar94/vimperator-labs,mcarton/vimperator-labs,airodactyl/airodactyl,paretje/vimperator-labs,mcarton/vimperator-labs,stemar94/vimperator-labs,derenio/vimperator-labs