Before revision:   We show that  there is no polynomial-time (\frac{3{2}-\varepsilon)-approximation algorithm for any \varepsilon~>~0 }  unless \mathsf{P}=\mathsf{NP}.
After revision:  We show that , if \ell is part of the input, then there is no polynomial-time (\frac{3{2}-\varepsilon)-approximation algorithm for any \varepsilon~>~0 } unless \mathsf{P}=\mathsf{NP}.