build: update list of dependencies

- I prefer to specify stable versions.
- Do not mention gettext, it's already a dependency of GLib.
- Forgot to add dconf to the README.

README

@@ -20,11 +20,11 @@ Dependencies
 
 * GLib >= 2.50
 * GTK+ >= 3.22
-* GtkSourceView >= 3.99.7
+* GtkSourceView >= 4.0
 * Tepl >= 3.99.1 - https://wiki.gnome.org/Projects/Tepl
 * gspell >= 1.0
 * gee-0.8 >= 0.10
-* gettext
+* dconf
 * gsettings-desktop-schemas
 * Latexmk >= 4.31 (optional, but strongly recommended)
 

configure.ac

@@ -31,7 +31,7 @@ LT_INIT
 # Update also the --target-glib option in src/Makefile.am.
 GLIB_REQUIRED_VERSION="2.50"
 GTK_REQUIRED_VERSION="3.22"
-GTKSOURCEVIEW_REQUIRED_VERSION="3.99.7"
+GTKSOURCEVIEW_REQUIRED_VERSION="4.0"
 TEPL_REQUIRED_VERSION="3.99.1"
 GSPELL_REQUIRED_VERSION="1.0"
 VALA_REQUIRED_VERSION="0.34"