Added function signature helpers to Decoder.java - Test update

src/test/java/com/github/wkennedy/abi/DecoderTest.java

@@ -180,7 +180,7 @@ public void testDecodeFunctionTupleContainingDynamicTypes() throws IOException {
     @Test
     public void testGetFunctionSignature() {
         String functionSignature = Decoder.getFunctionSignature("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");
-        assertEquals("0x73b80d49777f0c32d45a0a5a7c3487eb9e8da2c93922540c260cdafc3e81a165", functionSignature);
+        assertEquals("0xac9650d8", functionSignature);
     }
 
     @Test