Update to latest dlclark/regexp2.

Fixes #424.

Author: alecthomas

Diff for: go.mod

@@ -8,7 +8,7 @@ require (
 	github.com/alecthomas/kong v0.2.4
 	github.com/alecthomas/repr v0.0.0-20180818092828-117648cd9897 // indirect
 	github.com/danwakefield/fnmatch v0.0.0-20160403171240-cbb64ac3d964
-	github.com/dlclark/regexp2 v1.2.0
+	github.com/dlclark/regexp2 v1.4.0
 	github.com/mattn/go-colorable v0.1.6
 	github.com/mattn/go-isatty v0.0.12
 	github.com/pkg/errors v0.9.1 // indirect

Diff for: go.sum

@@ -13,6 +13,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dlclark/regexp2 v1.2.0 h1:8sAhBGEM0dRWogWqWyQeIJnxjWO6oIjl8FKqREDsGfk=
 github.com/dlclark/regexp2 v1.2.0/go.mod h1:2pZnwuY/m+8K6iRw6wQdMtk+rH5tNGR1i55kozfMjCc=
+github.com/dlclark/regexp2 v1.4.0 h1:F1rxgk7p4uKjwIQxBs9oAXe5CqrXlCduYEJvrF4u93E=
+github.com/dlclark/regexp2 v1.4.0/go.mod h1:2pZnwuY/m+8K6iRw6wQdMtk+rH5tNGR1i55kozfMjCc=
 github.com/mattn/go-colorable v0.1.6 h1:6Su7aK7lXmJ/U79bYtBjLNaha4Fs1Rg9plHpcH+vvnE=
 github.com/mattn/go-colorable v0.1.6/go.mod h1:u6P/XSegPjTcexA+o6vUJrdnUu04hMope9wVRipJSqc=
 github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHXY=