devel/bear: Update to 3.1.3

When building devel/bear, pkgconf 1.8.1 still seems to hang [0]. The
issue has been fixed upstream [1], and that fix will be included in a
pending update of devel/pkgconf [2].

[0] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=265542
[1] https://github.com/pkgconf/pkgconf/issues/229
[2] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=272934

Changes: https://github.com/rizsotto/Bear/releases/tag/3.1.3
Sponsored by: The FreeBSD Foundation