Renamed PangramTest to PangramsTest to be consistent with class it's testing.

exercises/pangram/src/test/java/PangramTest.java → exercises/pangram/src/test/java/PangramsTest.java

 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertFalse;
 
-public class PangramTest {
+public class PangramsTest {
 
 
     @Test