lapack/gonum: fix link to gonum/mat in package doc
// The full LAPACK capability has not been implemented at present. The full
// API is very large, containing approximately 200 functions for double precision
// alone. Future additions will be focused on supporting the Gonum matrix
-// package (https://godoc.org/github.com/gonum/matrix/mat64), though pull requests
+// package (https://godoc.org/gonum.org/v1/gonum/mat), though pull requests
// with implementations and tests for LAPACK function are encouraged.
package gonum // import "gonum.org/v1/gonum/lapack/gonum"
