Reduce number of string operations
Reduce number of string operations

Once Ruby 1.8.7 reaches end-of-life, we can remove the tr entirely by
using Base64.urlsafe_encode and -_decode (which are implemented in the
standard library by using tr in exactly this way).

zenjoy/ruby-jwt,JuanitoFatas/ruby-jwt,jwt/ruby-jwt,yahooguntu/ruby-jwt,tobscher/ruby-jwt,progrium/ruby-jwt,ernie/ruby-jwt,nycvotes-dev/ruby-jwt,skippy/ruby-jwt,larrylv/ruby-jwt,bkeepers/ruby-jwt,danoph/ruby-jwt,ab320012/ruby-jwt,sferik/ruby-jwt,aj-michael/ruby-jwt,iamjarvo/ruby-jwt,petergoldstein/ruby-jwt,tjmw/ruby-jwt,excpt/ruby-jwt