chore: 1.3.0

A browser no longer shows the "unsupported command-line flag" bar. It is given
--enable-features=MiddleClickAutoscroll, which asks for the same feature
without being on the list of flags Chromium warns about; everything that embeds
an older Chromium keeps the flag that works there, and shows no bar either way.

Helium gets its own name for the feature alongside it, so autoscroll works
there for the first time.

An installation from 1.2.0 or earlier is taken back and written again on the
next apply.

Makefile

@@ -8,7 +8,7 @@
 # Overridable so a packager can pass the version it is actually building
 # (`make VERSION=$pkgver`). The literal below is the fallback for builds
 # straight from a checkout, and is what a release tag has to carry.
-VERSION      ?= 1.2.0
+VERSION      ?= 1.3.0
 
 PREFIX       ?= /usr
 DESTDIR      ?=