Fix 2D array passed to Arrays.fill() (#2010)

Arrays.fill() accepts single dimensional arrays, so fill one row at a time.

Fixes TheAlgorithms/Java#2009

DataStructures/Graphs/FloydWarshall.java

@@ -14,7 +14,7 @@ public class FloydWarshall {
             [numberofvertices
                 + 1]; // stores the value of distance from all the possible path form the source
     // vertex to destination vertex
-    Arrays.fill(DistanceMatrix, 0);
+    // The matrix is initialized with 0's by default
     this.numberofvertices = numberofvertices;
   }