docs(ngBind): fix wording

You can not change the use of `{{}}`/`ngBind` based on the time when it is used.
So this should be "if".

Closes #7786

src/ng/directive/ngBind.js

@@ -13,7 +13,7 @@
  * Typically, you don't use `ngBind` directly, but instead you use the double curly markup like
  * `{{ expression }}` which is similar but less verbose.
  *
- * It is preferable to use `ngBind` instead of `{{ expression }}` when a template is momentarily
+ * It is preferable to use `ngBind` instead of `{{ expression }}` if a template is momentarily
  * displayed by the browser in its raw state before Angular compiles it. Since `ngBind` is an
  * element attribute, it makes the bindings invisible to the user while the page is loading.
  *