Attempt to fix build break on aix

terminal_check_aix.go

@@ -0,0 +1,9 @@
+// +build !appengine,!js,!windows,aix
+
+package logrus
+
+import "io"
+
+func checkIfTerminal(w io.Writer) bool {
+	return false
+}

terminal_check_notappengine.go

@@ -1,4 +1,4 @@
-// +build !appengine,!js,!windows
+// +build !appengine,!js,!windows,!aix
 
 package logrus