Make Flow#unshift_filter the primary alias before filter_prepend to be more consistent

lib/rackstash/flow.rb

@@ -166,11 +166,11 @@ module Rackstash
     end
 
     # (see FilterChain#unshift)
-    def filter_prepend(*filter, &block)
+    def filter_unshift(*filter, &block)
       @filter_chain.unshift(*filter, &block)
       self
     end
-    alias filter_unshift filter_prepend
+    alias filter_prepend filter_unshift
 
     # Re-open the log adapter if supported. This might be a no-op if the adapter
     # does not support reopening. This method is called by the logger's {Sink}.

spec/rackstash/flow_spec.rb

@@ -213,18 +213,18 @@ describe Rackstash::Flow do
     end
   end
 
-  describe '#filter_prepend' do
+  describe '#filter_unshift' do
     it 'calls FilterChain#unshift' do
       expect(flow.filter_chain).to receive(:unshift).twice.and_call_original
 
-      expect(flow.filter_prepend ->(event) { event }).to equal flow
+      expect(flow.filter_unshift ->(event) { event }).to equal flow
-      expect(flow.filter_prepend { |event| event }).to equal flow
+      expect(flow.filter_unshift { |event| event }).to equal flow
 
       expect(flow.filter_chain.size).to eql 2
     end
 
-    it 'can use the #filter_unshift alias' do
+    it 'can use the #filter_prepend alias' do
-      expect(flow.method(:filter_unshift)).to eql flow.method(:filter_prepend)
+      expect(flow.method(:filter_prepend)).to eql flow.method(:filter_unshift)
     end
   end