Change variable name.

This reduces the desire to use map! (instead of map) which would modify
the user's argument in-place. There's a test to prevent that but this
makes sense semantically too.

lib/geocoder/calculations.rb

@@ -118,11 +118,11 @@ module Geocoder
     def geographic_center(points)
 
       # convert objects to [lat,lon] arrays and convert degrees to radians
-      points = points.map{ |p| to_radians(extract_coordinates(p)) }
+      coords = points.map{ |p| to_radians(extract_coordinates(p)) }
 
       # convert to Cartesian coordinates
       x = []; y = []; z = []
-      points.each do |p|
+      coords.each do |p|
         x << Math.cos(p[0]) * Math.cos(p[1])
         y << Math.cos(p[0]) * Math.sin(p[1])
         z << Math.sin(p[0])