update go-internal to fix go 1.16

CI's gotip job should now succeed.

go.mod

@@ -4,7 +4,7 @@ go 1.15
 
 require (
 	github.com/google/go-cmp v0.5.2
-	github.com/rogpeppe/go-internal v1.6.1
+	github.com/rogpeppe/go-internal v1.6.2-0.20200830194709-1115b6af0369
 	golang.org/x/mod v0.3.1-0.20200828183125-ce943fd02449
 	golang.org/x/tools v0.0.0-20200828161849-5deb26317202
 )

go.sum

@@ -5,8 +5,8 @@ github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORN
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
-github.com/rogpeppe/go-internal v1.6.1 h1:/FiVV8dS/e+YqF2JvO3yXRFbBLTIuSDkuC7aBOAvL+k=
-github.com/rogpeppe/go-internal v1.6.1/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=
+github.com/rogpeppe/go-internal v1.6.2-0.20200830194709-1115b6af0369 h1:wdCVGtPadWC/ZuuLC7Hv58VQ5UF7V98ewE71n5mJfrM=
+github.com/rogpeppe/go-internal v1.6.2-0.20200830194709-1115b6af0369/go.mod h1:xXDCJY+GAPziupqXw64V24skbSoqbTEfhy4qGm1nDQc=
 github.com/yuin/goldmark v1.1.32/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=