fix some typos found in activemodel

activemodel/test/cases/callbacks_test.rb

@@ -107,7 +107,7 @@ class Violin2 < Violin
   test "after_create callbacks with both callbacks declared in one line" do
     assert_equal ["callback1", "callback2"], Violin1.new.create.history
   end
-  test "after_create callbacks with both callbacks declared in differnt lines" do
+  test "after_create callbacks with both callbacks declared in different lines" do
     assert_equal ["callback1", "callback2"], Violin2.new.create.history
   end
 

activemodel/test/cases/validations/with_validation_test.rb

@@ -50,7 +50,7 @@ def check_validity!
     end
   end
 
-  test "vaidation with class that adds errors" do
+  test "validation with class that adds errors" do
     Topic.validates_with(ValidatorThatAddsErrors)
     topic = Topic.new
     assert topic.invalid?, "A class that adds errors causes the record to be invalid"

activemodel/test/cases/validations_test.rb

@@ -26,11 +26,11 @@ def teardown
   def test_single_field_validation
     r = Reply.new
     r.title = "There's no content!"
-    assert r.invalid?, "A reply without content shouldn't be saveable"
+    assert r.invalid?, "A reply without content shouldn't be savable"
     assert r.after_validation_performed, "after_validation callback should be called"
 
     r.content = "Messa content!"
-    assert r.valid?, "A reply with content should be saveable"
+    assert r.valid?, "A reply with content should be savable"
     assert r.after_validation_performed, "after_validation callback should be called"
   end