docs: fix ContainSubstring references (#673)

Author: williandandrade

docs/index.md

@@ -1510,7 +1510,7 @@ Here are some examples:
 - `Expect(resp).To(HaveHTTPHeaderWithValue("Content-Type", "application/json"))`:
     asserts that the `Content-Type` header has exactly the value `application/json`.
 
-- `Expect(resp).To(HaveHTTPHeaderWithValue(ContainsSubstring("json")))`:
+- `Expect(resp).To(HaveHTTPHeaderWithValue(ContainSubstring("json")))`:
     asserts that the `Content-Type` header contains the substring `json`.
 
 ### Asserting on Panics

matchers.go

@@ -92,9 +92,9 @@ func Succeed() types.GomegaMatcher {
 //
 // These are valid use-cases:
 //
-//  Expect(err).Should(MatchError("an error")) //asserts that err.Error() == "an error"
-//  Expect(err).Should(MatchError(SomeError)) //asserts that err == SomeError (via reflect.DeepEqual)
-//  Expect(err).Should(MatchError(ContainsSubstring("sprocket not found"))) // asserts that edrr.Error() contains substring "sprocket not found"
+//	Expect(err).Should(MatchError("an error")) //asserts that err.Error() == "an error"
+//	Expect(err).Should(MatchError(SomeError)) //asserts that err == SomeError (via reflect.DeepEqual)
+//	Expect(err).Should(MatchError(ContainSubstring("sprocket not found"))) // asserts that edrr.Error() contains substring "sprocket not found"
 //
 // It is an error for err to be nil or an object that does not implement the
 // Error interface