Adding build failed fixes.

Author: the-yash-rajput

src/main/java/com/thealgorithms/graph/TopologicalSort.java

@@ -16,6 +16,10 @@
  */
 public final class TopologicalSort {
 
+    private TopologicalSort() {
+        throw new AssertionError("No instances.");
+    }
+
     /**
      * Class that represents a directed graph and provides methods for
      * manipulating the graph