Simplify go code

Just reads a bit nicer, in my opinion.

assert/assertions_test.go

@@ -2205,7 +2205,7 @@ func TestEventuallyTrue(t *testing.T) {
 	state := 0
 	condition := func() bool {
 		defer func() {
-			state = state + 1
+			state += 1
 		}()
 		return state == 2
 	}

http/test_response_writer.go

@@ -36,7 +36,7 @@ func (rw *TestResponseWriter) Write(bytes []byte) (int, error) {
 	}
 
 	// add these bytes to the output string
-	rw.Output = rw.Output + string(bytes)
+	rw.Output += string(bytes)
 
 	// return normal values
 	return 0, nil