Fix errors the occur when attempting to use a Gaga instance that is c…

…reated without specifying a branch.

lib/gaga.rb

@@ -121,7 +121,7 @@ def git
 
   # The git branch to use for this store
   def branch
-    @options[:branch].to_s || 'master'
+    (@options[:branch] || 'master').to_s
   end
 
   # Checks out the branch on the repo

test/gaga_test.rb

@@ -27,6 +27,16 @@
     it "reads from keys" do
       @store[key].must_be_nil
     end
+
+    it "should default to master when no branch is specified" do
+      value = 'testing'
+      @master[key] = value
+      @master[key].must_equal value
+      @store[key].must_be_nil
+
+      tmp = Gaga.new(:repo => tmp_dir, :branch => :master)
+      tmp[key].must_equal value
+    end
 
     it 'guarantess the key is stored in the right branch' do
       @store[key] = 'value'