Square Root Symbol

Sometimes, the symbol of square root is not returning correctly. So, to be sure, I replaced that with `sqrt`.

Author: jfullstackdev

src/simplejavacalculator/UI.java

@@ -91,7 +91,7 @@ public UI() {
       butMultiply = new JButton("*");      
       butDivide = new JButton("/");      
       butEqual = new JButton("=");      
-      butSquareRoot = new JButton("√");      
+      butSquareRoot = new JButton("sqrt");      
       butSquare = new JButton("x*x");      
       butOneDevidedBy = new JButton("1/x");      
       butCos = new JButton("Cos");