Makefile: Release to both 1.10 and 1.11 servers.

The Makefile’s `release` target only released to one add-ons server — by
default, the official 1.11.x add-ons server.

This commit changes the Makefile so that the `release` target releases
to both the 1.10.x and 1.11.x official add-ons servers.
release.zsh: Drop filename extension.

Drop `scripts/release.zsh`’s filename extension (`.zsh`).