Use channels over WaitGroup in needsUpdate()

Using a WaitGroup forced the code to wait for every goroutine to finish.
Using channels allows us to exit early if any of a packages sources need
an update. No point in waiting for the other requests to finish if we
know there is an update.

vcs.go

@@ -6,7 +6,6 @@ import (
 	"os"
 	"os/exec"
 	"strings"
-	"sync"
 	"time"
 )
 
@@ -143,25 +142,38 @@ func getCommit(url string, branch string, protocols []string) string {
 }
 
 func (infos shaInfos) needsUpdate() bool {
-	var wg sync.WaitGroup
-	hasUpdate := false
+	//used to signal we have gone through all sources and found nothing
+	finished := make(chan struct{})
+	alive := 0
+	
+	//if we find an update we use this to exit early and return true
+	hasUpdate := make(chan struct{})
 
 	checkHash := func(url string, info shaInfo) {
-		defer wg.Done()
 		hash := getCommit(url, info.Brach, info.Protocols)
 		if hash != "" && hash != info.SHA {
-			hasUpdate = true
+			hasUpdate <- struct{}{}
+		} else {
+			finished <- struct{}{}
 		}
 	}
 
 	for url, info := range infos {
-		wg.Add(1)
+		alive++
 		go checkHash(url, info)
 	}
 
-	wg.Wait()
-
-	return hasUpdate
+	for {
+		select {
+		case <- hasUpdate:
+			return true
+		case <- finished:
+			alive--
+			if alive == 0 {
+				return false
+			}
+		}
+	}
 }
 
 func inStore(pkgName string) shaInfos {