Singular.jl 0.13.1 released

Today Singular.jl 0.13.1 has been released.

Diff since v0.13.0

Merged pull requests:

• Update maintainer docs (#591) (@tthsqe12)
• bump libsingular_julia_jll and Singular_jll dependencies (#592) (@YueRen)
• bump to 0.13.1 (#593) (@YueRen)