Redmine

Hello ,

I am trying to migrate & upgrade the redmine version from v 1.2.1 to v 2.5.x. Everytime i get the error " ERROR: Failed to build gem native extension." related to gems.
Earlier there was the error related to pg gem. Now the error is for Json.

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory: /var/lib/gems/2.3.0/gems/json-1.8.6/ext/json/ext/generator
/usr/bin/ruby2.3 -r ./siteconf20171107-1831-15dcj94.rb extconf.rb
creating Makefile

current directory: /var/lib/gems/2.3.0/gems/json-1.8.6/ext/json/ext/generator
make "DESTDIR=" clean
sh: 1: make: not found

current directory: /var/lib/gems/2.3.0/gems/json-1.8.6/ext/json/ext/generator
make "DESTDIR="
sh: 1: make: not found

make failed, exit code 127

Gem files will remain installed in /var/lib/gems/2.3.0/gems/json-1.8.6 for inspection.
Results logged to /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/json-1.8.6/gem_make.out

An error occurred while installing json (1.8.6), and Bundler cannot continue.
Make sure that `gem install json -v '1.8.6'` succeeds before bundling.

In Gemfile:
jquery-rails was resolved to 2.0.3, which depends on
railties was resolved to 3.2.19, which depends on
rdoc was resolved to 3.12.2, which depends on
json