Bump version 40.0

NEWS

-News in 40.alpha, 2021-xx-yy (not yet released)
+News in 40, 2021-03-19
 ----------------------------
 * Remove all the deprecated API.
+* file-browser: drop use of confirm-trash
+* Translation updates.
 
 Tepl-ification:
 * Use tepl_pango_font_description_to_css().

meson.build

 project(
   'gedit', 'c',
-  version: '3.38.2',
+  version: '40.0',
   meson_version: '>= 0.53'
 )
 
@@ -13,7 +13,7 @@ i18n = import('i18n')
 pkg_config = import('pkgconfig')
 python = import('python')
 
-api_version = '3.38'
+api_version = '40.0'
 
 # Paths
 root_include_dir = include_directories('.')