Use SPDX full name of Apache License 2.0 (#9104)

https://spdx.org/licenses/Apache-2.0.html

- Full name: Apache License 2.0
- Short identifier: Apache-2.0

Author: chulkilee

README.md

@@ -209,6 +209,6 @@ the `doc` directory. If you are planning to contribute documentation,
 
 "Elixir" and the Elixir logo are copyright (c) 2012 Plataformatec.
 
-Elixir source code is released under Apache 2 License.
+Elixir source code is released under Apache License 2.0.
 
 Check [NOTICE](NOTICE) and [LICENSE](LICENSE) files for more information.

lib/elixir/pages/Library Guidelines.md

@@ -24,7 +24,7 @@ Writing code is only the first of many steps to publish a package. We strongly r
 
   * Choose a versioning schema. Elixir requires versions to be in the format `MAJOR.MINOR.PATCH` but the meaning of those numbers is up to you. Most projects choose [Semantic Versioning](https://semver.org/).
 
-  * Choose a [license](https://choosealicense.com/). The most common licenses in the Elixir community are the [MIT License](https://choosealicense.com/licenses/mit/) and the [Apache 2.0 License](https://choosealicense.com/licenses/apache-2.0/). The latter is also the one used by Elixir itself.
+  * Choose a [license](https://choosealicense.com/). The most common licenses in the Elixir community are the [MIT License](https://choosealicense.com/licenses/mit/) and the [Apache License 2.0](https://choosealicense.com/licenses/apache-2.0/). The latter is also the one used by Elixir itself.
 
   * Run the [code formatter](https://hexdocs.pm/mix/Mix.Tasks.Format.html). The code formatter formats your code according to a consistent style shared by your library and the whole community, making it easier for other developers to understand your code and contribute.