Use the editor font in the completion widget

This is pretty common in other editors, and the application font looks
weird if the text editor font is significantly larger.

Task-number: QTCREATORBUG-1424
Reviewed-by: Olivier Goffart

src/plugins/texteditor/completionwidget.cpp

@@ -153,6 +153,7 @@ CompletionWidget::CompletionWidget(CompletionSupport *support, ITextEditable *ed
     setObjectName(QLatin1String("m_popupFrame"));
     setAttribute(Qt::WA_DeleteOnClose);
     setMinimumSize(1, 1);
+    setFont(editor->widget()->font());
 
     QVBoxLayout *layout = new QVBoxLayout(this);
     layout->setMargin(0);