fix: missing migrations from plugins folder

Author: kaixoo

plugins/detect-indent/detect-indent.vala

@@ -17,7 +17,7 @@ public class Scratch.Plugins.DetectIndent: Peas.ExtensionBase, Peas.Activatable
                 return;
             }
 
-            var source_buffer = (Gtk.SourceBuffer) view.buffer;
+            var source_buffer = (GtkSource.Buffer) view.buffer;
             Gtk.TextIter it;
             source_buffer.get_iter_at_line (out it, 0);
 

plugins/highlight-word-selection/highlight-word-selection.vala

@@ -58,7 +58,7 @@ public class Scratch.Plugins.HighlightSelectedWords : Peas.ExtensionBase, Peas.A
             window_search_context.get_occurrences_count () == 0) {
             // Perform plugin selection when there is no ongoing and successful search 
             current_search_context = new Gtk.SourceSearchContext (
-                (Gtk.SourceBuffer)current_source.buffer,
+                (GtkSource.Buffer)current_source.buffer,
                 null
             );
             current_search_context.settings.search_text = "";

plugins/spell/spell.vala

@@ -98,7 +98,7 @@ public class Scratch.Plugins.Spell: Peas.ExtensionBase, Peas.Activatable {
                 });
 
                 // Deactivate Spell checker when we are editing a code file
-                var source_buffer = (Gtk.SourceBuffer) d.source_view.buffer;
+                var source_buffer = (GtkSource.Buffer) d.source_view.buffer;
                 var lang = source_buffer.language;
                 if (lang != null && lang.id != "markdown") {
                     spell.detach ();