Parser bug

[PoslavskySV]

Test case

@Test
public void test16() {
    Coder<UnivariatePolynomial<Rational<BigInteger>>, ?, ?> coder = Coder.mkUnivariateCoder(UnivariateRing(Q), "x");
    assertEquals(coder.parse("-1 + (2*x)^4"), coder.parse("-1 + 2^4*x^4"));
}