Fix typo

src/lib/autocomplete/autocomplete-trigger.ts

@@ -359,7 +359,7 @@ export class MdAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
   private _setTriggerValue(value: any): void {
     const toDisplay = this.autocomplete.displayWith ? this.autocomplete.displayWith(value) : value;
     // Simply falling back to an empty string if the display value is falsy does not work properly.
-    // The display value can also be the number zero and shouldn't fallback to an empty string.
+    // The display value can also be the number zero and shouldn't fall back to an empty string.
     this._element.nativeElement.value = toDisplay != null ? toDisplay : '';
   }