magmasource/alphaMELTS: v2.3.1

When v2.3.0 was released some older file versions were included in the .zip archives by accident. Notably among these was install.command, which had a bug that had been corrected elsewhere (see Issue #1). Release v2.3.1 includes rebuilt and corrected files; it also updates the version numbers within the code and links are updated to point to GitHub.

The fluid phase is now consistently called 'fluid' everywhere in all thermodynamic models in alphaMELTS (previously was 'water' in Rhyolite-MELTS 1.0.2 and pMELTS, and 'fluid' in Rhyolite-MELTS 1.1.0 and 1.2.0).