change dependancies. nokogiri requires a later ruby now as pointed out here: https://github.com/openstreetmap/openstreetmap-website/issues/1402 ruby2.0->ruby 2.3 ...which then entails a later ubuntu if we're installing from packages.
## Minimum requirements
-* Ruby 2.0
+* Ruby 2.3
* RubyGems 1.3.1+
* PostgreSQL 9.1+
* ImageMagick
* Bundler
* Javascript Runtime
-These can be installed on Ubuntu 14.04 or later with:
+These can be installed on Ubuntu 16.04 or later with:
```
-sudo apt-get install ruby2.0 libruby2.0 ruby2.0-dev \
+sudo apt-get install ruby2.3 libruby2.3 ruby2.3-dev \
libmagickwand-dev libxml2-dev libxslt1-dev nodejs \
apache2 apache2-threaded-dev build-essential git-core \
postgresql postgresql-contrib libpq-dev postgresql-server-dev-all \