support for plugins where the init method doesn't return a Promise

plugin/highlight/highlight.js

@@ -97,8 +97,6 @@ c:[{cN:"comment",b:/\(\*/,e:/\*\)/},e.ASM,e.QSM,e.CNM,{b:/\{/,e:/\}/,i:/:/}]}});
 				}
 			} );
 
-			return Promise.resolve();
-
 		},
 
 		/**

plugin/math/math.js

@@ -84,8 +84,6 @@ var RevealMath = window.RevealMath || (function(){
 
 			} );
 
-			return Promise.resolve();
-
 		}
 	}
 

plugin/notes/notes.js

@@ -168,8 +168,6 @@ var RevealNotes = (function() {
 
 			}
 
-			return Promise.resolve();
-
 		},
 
 		open: openNotes

plugin/zoom-js/zoom.js

@@ -22,8 +22,6 @@ var RevealZoom = (function(){
 				}
 			} );
 
-			return Promise.resolve();
-
 		}
 	}