Fix package license to be a valid SPDX identifier

[typerandom]

Fixes so that the package version is a valid SPDX identifier (see https://spdx.org/licenses/Apache-2.0.html).

How to verify

1. Checkout the master branch.
2. Remove the node_modules directory.
3. Run $ npm install.
4. Verify that you see the warning npm WARN [email protected] license should be a valid SPDX license expression.
5. Checkout this branch.
6. Remove the node_modules directory.
7. Run $ npm install.
8. Verify that you don't see the npm WARN [email protected] license should be a valid SPDX license expression warning.

[coveralls]

Coverage remained the same at 100.0% when pulling e340fe1 on fix-package-version into 5edb076 on master.

[robertjd]

Verified