Fix typos in few files

CONTRIBUTING.md

@@ -81,7 +81,7 @@ can use to either 'zoom out' fully and see everything that is front of you, or y
 The only difference is that in case of viewports there is no actual zooming in but only
 demarcation of areas within the canvas that are to treated as the 'world'.
 
-The implication on rubyplot would be that an `Axes` within a `Figure` would get mappped
+The implication on rubyplot would be that an `Axes` within a `Figure` would get mapped
 to a `viewport` and the plotting within the viewport would take place by setting up the
 world co-ordinates to between the X and Y range.
 

lib/rubyplot.rb

@@ -1,7 +1,5 @@
 require 'bigdecimal'
-
 require 'rmagick'
-
 require 'rubyplot/color'
 require 'rubyplot/utils'
 require 'rubyplot/version'

lib/rubyplot/artist/axes.rb

@@ -317,5 +317,5 @@ def set_yrange
         @y_axis.max_val = @y_range[1]
       end
     end # class Axes
-  end # moudle Artist
+  end # module Artist
 end # module Rubyplot