fix rake gems:install task

Rakefile

@@ -1,4 +1,3 @@
-require 'environment'
 require 'spec/rake/spectask'
 
 task :default => :test
@@ -16,12 +15,12 @@ end
 
 namespace :db do
   desc 'Auto-migrate the database (destroys data)'
-  task :migrate do
+  task :migrate => :environment do
     DataMapper.auto_migrate!
   end
 
   desc 'Auto-upgrade the database (preserves data)'
-  task :upgrade do
+  task :upgrade => :environment do
     DataMapper.auto_upgrade!
   end
 end
@@ -34,3 +33,7 @@ namespace :gems do
     required_gems.each { |required_gem| system "sudo gem install #{required_gem}" }
   end
 end
+
+task :environment do
+  require 'environment'
+end