Fix typo in page title (emmitters -> emitters) (#127)

docs/modules/core/pages/effect/particle_emitters.adoc

@@ -1,4 +1,4 @@
-= Particle Emmitter Settings
+= Particle Emitter Settings
 :revnumber: 2.2
 :revdate: 2020/07/24
 :keywords: documentation, effect