Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension. /home/hash/.rvm/rubies/ruby-1.9.3-p327/bin/ruby extconf.rb checking for pg_config... no No pg_config... trying anyway. If building fails, please try again with --with-pg-config=/path/to/pg_config checking for libpq-fe.h... no Can't find the 'libpq-fe.h header *** extconf.rb failed ***