hamming: remove signature for unchecked exceptions [Fix #304]

exercises/hamming/src/test/java/HammingTest.java

 
     @Ignore
     @Test
-    public void testValidatesFirstStrandNotLonger() throws IllegalArgumentException {
+    public void testValidatesFirstStrandNotLonger() {
         thrown.expect(IllegalArgumentException.class);
         Hamming.compute("AAAG", "AAA");                
     }
 
     @Ignore
     @Test
-    public void testValidatesOtherStrandNotLonger() throws IllegalArgumentException {
+    public void testValidatesOtherStrandNotLonger() {
         thrown.expect(IllegalArgumentException.class);
         Hamming.compute("AAA", "AAAG");
     }