[meson] Rename 'gtk_doc' option to 'docs'

diff --git a/meson_options.txt b/meson_options.txt
index 5ef7709..8bc190b 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -25,7 +25,7 @@
   description: 'Enable or disable unit tests')
 option('introspection', type: 'feature', value: 'auto', yield: true,
   description: 'Generate gobject-introspection bindings (.gir/.typelib files)')
-option('gtk_doc',  type: 'feature', value: 'auto', yield: true,
+option('docs', type: 'feature', value: 'auto', yield: true,
   description: 'Generate documentation with gtk-doc')
 
 option('benchmark', type: 'feature', value: 'auto',