Fix anchor links in INSTALL.md

GitLab converts " / " to "-", unlike GitHub's "--"

docs/INSTALL.md

@@ -6,18 +6,18 @@ but compiling on Windows and macOS should be possible with the right tools.
 - [Packages](#packages)
   - [Linux](#linux)
     - [Flatpak](#flatpak)
-    - [Alpine Linux / postmarketOS](#alpine-linux--postmarketOS)
+    - [Alpine Linux / postmarketOS](#alpine-linux-postmarketOS)
     - [Arch Linux](#arch-linux)
 - [Manual installation](#manual-installation)
   - [Environment variables](#environment-variables)
   - [Package manager dependencies](#package-manager-dependencies)
-    - [Alpine Linux 3.9+ / apk](#alpine-linux-39--apk)
-    - [Arch Linux / pacman & AUR](#arch-linux--pacman--aur)
-    - [Fedora 30+ / dnf](#fedora-30--dnf)
-    - [Gentoo / emerge](#gentoo--emerge)
-    - [Ubuntu 19.04 / apt](#ubuntu-1904--apt)
-    - [Ubuntu 19.10+, Debian bullseye / apt](#ubuntu-1910-debian-bullseye--apt)
-    - [Void Linux / xbps](#void-linux--xbps)
+    - [Alpine Linux 3.9+ / apk](#alpine-linux-39-apk)
+    - [Arch Linux / pacman & AUR](#arch-linux-pacman-aur)
+    - [Fedora 30+ / dnf](#fedora-30-dnf)
+    - [Gentoo / emerge](#gentoo-emerge)
+    - [Ubuntu 19.04 / apt](#ubuntu-1904-apt)
+    - [Ubuntu 19.10+, Debian bullseye / apt](#ubuntu-1910-debian-bullseye-apt)
+    - [Void Linux / xbps](#void-linux-xbps)
   - [Installing PyOtherSide manually](#installing-pyotherside-manually)
   - [Installing libolm manually](#installing-libolm-manually)
   - [Installing or updating Moment](#installing-or-updating-moment)