Adds ability for concentrations to convert to a scalar denom uom

lib/unit/concentration.rb

@@ -37,7 +37,12 @@ def convert_to(uom)
       if uoms.size  <= 1
         raise IncompatibleUnitsError
       end
-      Concentration.new(numerator.convert_to(uoms[0]), denominator.convert_to(uoms[1]))
+      tokens = Lexer.new.tokenize("1 #{uom}")
+      destination_conc = Parser.new.parse(tokens)
+      Concentration.new(
+        numerator.convert_to(destination_conc.numerator.uom).scale(destination_conc.scalar), 
+        denominator.convert_to(destination_conc.denominator.uom)
+      )
     end
     alias_method :>>, :convert_to
 

test/concentration_test.rb

@@ -237,6 +237,12 @@ class ConcentrationTest < Minitest::Test
       assert_equal 2000, new_con.scalar
       assert_equal 'mcg/ml', new_con.uom
     end
+
+    should "convert to unit with scalar in denomatinor" do
+      new_con = @con >> 'mg/2ml'
+      assert_equal 1, new_con.scalar
+      assert_equal 'mg/ml', new_con.uom
+    end
   end
 
   context "abs" do