don't match newline at end of CallNumber

spec/value/call_number_spec.rb

@@ -33,6 +33,7 @@ module Chibrary
      expect { CallNumber.new('asdf--12') }.to raise_error(InvalidCallNumber)
      expect { CallNumber.new('asdf__12') }.to raise_error(InvalidCallNumber)
      expect { CallNumber.new('asdf"\'12') }.to raise_error(InvalidCallNumber)
      expect { CallNumber.new("asdf1234\n") }.to raise_error(InvalidCallNumber)
    end
  end

value/call_number.rb

@@ -17,7 +17,7 @@ def initialize str
  end

  def valid?
    str =~ /\A[a-zA-Z0-9]{8}\Z/
    str =~ /\A[a-zA-Z0-9]{8}\z/
  end

  def == other