Rename config setting from :maxminddb_gem to :lib.

README.md

@@ -735,7 +735,7 @@ You must add either the *[hive_geoip2](https://rubygems.org/gems/hive_geoip2)* g
     Geocoder.configure(
       ip_lookup: :geoip2, 
       geoip2: {
-        maxminddb_gem: 'hive_geoip2',
+        lib: 'hive_geoip2',
         file: File.join('folder', 'GeoLite2-City.mmdb')
       }
     )

lib/geocoder/lookups/geoip2.rb

@@ -7,7 +7,7 @@ module Geocoder
       def initialize
         unless configuration[:file].nil?
           begin
-            @gem_name = configuration[:maxminddb_gem] || 'maxminddb'
+            @gem_name = configuration[:lib] || 'maxminddb'
             require @gem_name
           rescue LoadError
             raise "Could not load Maxmind DB dependency. To use the GeoIP2 lookup you must add the #{@gem_name} gem to your Gemfile or have it installed in your system."