simple-application.md: consistent use of type=submit (#2657)

When following tutorial and typing everything in, I was confused that Save button didn't work. Turned out that tutorial switches type from "button" to "submit", which I haven't spotted. Perhaps it should had been "submit" from start?

docs/simple-application.md

@@ -341,7 +341,7 @@ module.exports = {
 			m("input.input[type=text][placeholder=First name]"),
 			m("label.label", "Last name"),
 			m("input.input[placeholder=Last name]"),
-			m("button.button[type=button]", "Save"),
+			m("button.button[type=submit]", "Save"),
 		])
 	}
 }
@@ -480,7 +480,7 @@ module.exports = {
 			m("input.input[type=text][placeholder=First name]", {value: User.current.firstName}),
 			m("label.label", "Last name"),
 			m("input.input[placeholder=Last name]", {value: User.current.lastName}),
-			m("button.button[type=button]", "Save"),
+			m("button.button[type=submit]", "Save"),
 		])
 	}
 }