difference-of-squares: renamed instance method

exercises/difference-of-squares/src/example/java/DifferenceOfSquaresCalculator.java

                 .sum();
     }
 
-    public int betweenSquareOfSumAndSumOfSquaresTo(final int input) {
+    public int computeDifferenceOfSquares(final int input) {
         return computeSquareOfSumTo(input) - computeSumOfSquaresTo(input);
     }
 

exercises/difference-of-squares/src/test/java/DifferenceOfSquaresCalculatorTest.java

     @Test
     public void testDifferenceOfSquares0() {
         final int expected = 0;
-        final int actual = calculator.betweenSquareOfSumAndSumOfSquaresTo(0);
+        final int actual = calculator.computeDifferenceOfSquares(0);
         assertEquals(expected, actual);
     }
 
     @Test
     public void testDifferenceOfSquares5() {
         final int expected = 170;
-        final int actual = calculator.betweenSquareOfSumAndSumOfSquaresTo(5);
+        final int actual = calculator.computeDifferenceOfSquares(5);
         assertEquals(expected, actual);
     }
 
     @Test
     public void testDifferenceOfSquares10() {
         final int expected = 2640;
-        final int actual = calculator.betweenSquareOfSumAndSumOfSquaresTo(10);
+        final int actual = calculator.computeDifferenceOfSquares(10);
         assertEquals(expected, actual);
     }
 
     @Test
     public void testDifferenceOfSquares100() {
         final int expected = 25164150;
-        final int actual = calculator.betweenSquareOfSumAndSumOfSquaresTo(100);
+        final int actual = calculator.computeDifferenceOfSquares(100);
         assertEquals(expected, actual);
     }