Migration downloads individual migration binaries

When performing a migration after installing a new ipfs version, ipfs-update finds the necessary mirgations, downloads the latest version of them from the distribution site, unpacks the executables, and runs the migrations in order.  It uses the code located in go-ipfs/repo/fsrepo/migrations to do this.

Also used go-ipfs/repo/fsrepo/migrations
- fetching binaries for things other than migrations
- fetching version information about binaries other than migrations
- looking at current repo version
- checking for local ipfs api availability

config/config.go

@@ -10,13 +10,3 @@ const CurrentVersionNumber = "1.6.1-dev"
 // It might not be currently available, but it might be later if we
 // add a Makefile and set it as a ldflag in the Makefile.
 var CurrentCommit string
-
-func GetUserAgent() string {
-	ua := CurrentAppName + "/" + CurrentVersionNumber
-
-	if CurrentCommit != "" {
-		ua += "-" + CurrentCommit
-	}
-
-	return ua
-}

go.mod

@@ -1,12 +1,11 @@
 module github.com/ipfs/ipfs-update
 
-go 1.12
+go 1.14
 
 require (
 	github.com/blang/semver v3.5.1+incompatible
-	github.com/coreos/go-semver v0.3.0
-	github.com/ipfs/go-ipfs-api v0.0.2
-	github.com/urfave/cli v1.22.1
+	github.com/ipfs/go-ipfs v0.7.1-0.20210112040606-bc5ef0c221e5
+	github.com/urfave/cli/v2 v2.3.0
 	github.com/whyrusleeping/stump v0.0.0-20160611222256-206f8f13aae1
-	golang.org/x/sys v0.0.0-20191118133127-cf1e2d577169
+	golang.org/x/sys v0.0.0-20200615200032-f1bc736245b1
 )