Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -32,7 +32,7 @@ Contributions are welcome and accepted. Please create issues or pull requests!
 * Always use `@Throws` when applicable, including the `@throws` KDoc tag.
 * Prefer descriptive type parameter names; for example, `Key` and `Value` are better than `K` and `V`.
     * Prefer an existing type variable convention  (`K` and `V` for maps) over creating your own.
-* Except for `: Any`, prefer usinf `where` for type variables.
+* Except for `: Any`, prefer using `where` for type variables.
 * For type variables, prefer using `T & Any` over `T : Any`, unless you use a type that explicitly bounds `T` to extend `Any` (not be nullable).
 
 #### Interfaces, Functional Interfaces, or Typealiases