Fix typos (#126)

Author: tagliala

test/mini_magick_test.rb

@@ -421,7 +421,7 @@
       @pipeline = ImageProcessing::MiniMagick.source(@portrait)
     end
 
-    it "rotates the image by specifed number of degrees" do
+    it "rotates the image by specified number of degrees" do
       assert_dimensions [600, 800], @pipeline.rotate!(0)
       assert_dimensions [800, 600], @pipeline.rotate!(90)
       assert_dimensions [600, 800], @pipeline.rotate!("180")

test/vips_test.rb

@@ -394,7 +394,7 @@
       @pipeline = ImageProcessing::Vips.source(@portrait)
     end
 
-    it "rotates by muliples of 90" do
+    it "rotates by multiples of 90" do
       assert_dimensions [600, 800], @pipeline.rotate!(0)
       assert_dimensions [800, 600], @pipeline.rotate!(90)
       assert_dimensions [600, 800], @pipeline.rotate!(180)