Added 'eps' in optimize.show_options for L-BFGS-B

In scipy.optimize.minimize, when algorithm is L-BFGS-B, there is an
option called eps. However, this options is missing if we use
scipy.optimize.show_options('minimize', 'L-BFGS-B') to look up its
options.
Merge pull request #3427 from yw5aj/master

Added 'eps' in scipy.optimize.show_options for L-BFGS-B