Move geoip gem check to the initialize function.

Lookups are always loaded even when they aren't used. So the geoip gem was being checked even when user wouldn't like to use the maxmind_local lookup.

lib/geocoder/lookups/maxmind_local.rb

 require 'geocoder/lookups/base'
 require 'geocoder/results/maxmind_local'
 
-begin
-  require 'geoip'
-rescue LoadError => e
-  raise 'Could not load geoip dependency. To use MaxMind Local lookup you must add geoip gem to your Gemfile or have it installed in your system.'
-end
-
 module Geocoder::Lookup
   class MaxmindLocal < Base
 
+    def initialize
+      begin
+        require 'geoip'
+      rescue LoadError => e
+        raise 'Could not load geoip dependency. To use MaxMind Local lookup you must add geoip gem to your Gemfile or have it installed in your system.'
+      end
+
+      super
+    end
+
     def name
       "MaxMind Local"
     end