Set version in source code (google#295)

Set the release version in the source code. 

An alternative to setting the version directly in source code is to get
package repositories to build their osv-scanner with goreleaser instead
of go directly. While goreleaser is often already in most repositories,
it is not as straightforward:

- Package repositories sometimes have their own guidelines for how to
build go, e.g. Arch Linux go binaries must be built with hardened
options which we currently do not do with goreleaser.
- goreleaser also expects to be in a git repository (to get version
tags), but most build systems prefers downloading the source code in a
tarball instead of checking out the repository.

Author: another-rex

cmd/osv-scanner/main.go

@@ -13,7 +13,8 @@ import (
 )
 
 var (
-	version = "dev"
+	// Update this variable when doing a release
+	version = "1.2.0"
 	commit  = "n/a"
 	date    = "n/a"
 )

cmd/osv-scanner/main_test.go

@@ -118,7 +118,7 @@ func TestRun(t *testing.T) {
 			args:         []string{"", "--version"},
 			wantExitCode: 0,
 			wantStdout: `
-				osv-scanner version: dev
+				osv-scanner version: 1.2.0
 				commit: n/a
 				built at: n/a
 			`,