Update README.md with AL 2.0

[focbenz]

Following PR #72 shortened the Apache License, Version 2.0 to "AL":

The Apache License, 2.0 should be abbreviated as AL instead of ASL. (https://www.apache.org/licenses/LICENSE-2.0)

Only the version 1.1 was known as Apache Software License 1.1, however, AL 2.0 can also be used for non-software. To avoid any confusion (e.g. in downstream licence checks), the abbreviation should be kept consistent.

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[michaelklishin]

Thank you!