Fixed the Goto Next/Previous Line actions

Due to the wrong enumerators being used, it was impossible to define
custom shortcuts for these actions.

Reviewed-by: mae
Task-number: QTCREATORBUG-2139

src/plugins/texteditor/basetexteditor.cpp

@@ -760,22 +760,22 @@ void BaseTextEditor::gotoLineEndWithSelection()
 
 void BaseTextEditor::gotoNextLine()
 {
-    moveCursor(QTextCursor::NextRow);
+    moveCursor(QTextCursor::Down);
 }
 
 void BaseTextEditor::gotoNextLineWithSelection()
 {
-    moveCursor(QTextCursor::NextRow, QTextCursor::KeepAnchor);
+    moveCursor(QTextCursor::Down, QTextCursor::KeepAnchor);
 }
 
 void BaseTextEditor::gotoPreviousLine()
 {
-    moveCursor(QTextCursor::PreviousRow);
+    moveCursor(QTextCursor::Up);
 }
 
 void BaseTextEditor::gotoPreviousLineWithSelection()
 {
-    moveCursor(QTextCursor::PreviousRow, QTextCursor::KeepAnchor);
+    moveCursor(QTextCursor::Up, QTextCursor::KeepAnchor);
 }
 
 void BaseTextEditor::gotoPreviousCharacter()