mercury-parser was renamed

[materemias]

as stated here project has been renamed to @postlight/parser. Install using @postlight/parser instead.
this makes the node image failed to build/install

[samuelclay]

This is fixed in the discover branch: https://github.com/samuelclay/NewsBlur/blob/discover/node/package.json#L7

I'll be merging it in soon, hopefully within the month. It's been up on staging.newsblur.com and it's working great.