Fix default hotkeys commands for splitting lines

These commands were revamped in 0ef9963 but the default hotkeys were
never updated. The hotkeys were automatically migrated, but resetting
the settings back to defaults would still set invalid settings.

src/libresrc/default_hotkey.json

@@ -125,10 +125,10 @@
 		"edit/line/delete" : [
 			"Ctrl-Delete"
 		],
-		"edit/line/duplicate/shift" : [
+		"edit/line/split/before" : [
 			"Ctrl-D"
 		],
-		"edit/line/duplicate/shift_back" : [
+		"edit/line/split/after" : [
 			"Ctrl-Shift-D"
 		],
 		"edit/line/paste" : [

src/libresrc/osx/default_hotkey.json

@@ -128,10 +128,10 @@
 		"edit/line/delete" : [
 			"Ctrl-Backspace"
 		],
-		"edit/line/duplicate/shift" : [
+		"edit/line/split/before" : [
 			"Ctrl-D"
 		],
-		"edit/line/duplicate/shift_back" : [
+		"edit/line/split/after" : [
 			"Ctrl-Shift-D"
 		],
 		"edit/line/paste" : [