Update lib/gruff/base.rb
Update lib/gruff/base.rb

add method to display the legend under the graph
jbcden/gruff,house9/gruff,vigetlabs/gruff,topfunky/gruff,MentalPower/gruff,philipgiuliani/gruff,innoq/gruff,iox/gruff,topfunky/gruff,isozaki/gruff,jrmhaig/gruff