Fix deprecated QRegExp

Use QRegularExpression instead.

https://doc.qt.io/qt-5/qregularexpression.html#notes-for-qregexp-users

This function was introduced in Qt 5

sources/diagramposition.cpp

@@ -1,17 +1,17 @@
 /*
 	Copyright 2006-2020 The QElectroTech Team
 	This file is part of QElectroTech.
-	
+
 	QElectroTech is free software: you can redistribute it and/or modify
 	it under the terms of the GNU General Public License as published by
 	the Free Software Foundation, either version 2 of the License, or
 	(at your option) any later version.
-	
+
 	QElectroTech is distributed in the hope that it will be useful,
 	but WITHOUT ANY WARRANTY; without even the implied warranty of
 	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 	GNU General Public License for more details.
-	
+
 	You should have received a copy of the GNU General Public License
 	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
 */
@@ -29,7 +29,7 @@
 DiagramPosition::DiagramPosition(const QString &letter, unsigned int number) {
 	// purifie les lettres
 	letter_ = letter.toUpper();
-	letter_.remove(QRegExp("[^A-Z]"));
+	letter_.remove(QRegularExpression("[^A-Z]"));
 	number_ = number;
 }
 
@@ -64,7 +64,7 @@ QString DiagramPosition::toString()
 		return("-");
 	}
 	QSettings settings;
-	
+
 	if (settings.value("border-columns_0", true).toBool()){
 	return(QString("%1%2").arg(letter_).arg(number_ - 1));
 	}else{