Measurement of the Relative Branching Fraction of \boldmath $B_{s}^{0} \rightarrow J/\psi f_{0}(980), f_{0}(980) \rightarrow \p i^{+}\pi^{-}$ to $B_{s}^{0} \rightarrow J/\psi \phi, \phi \rightarrow K^{+}K^{-}$