tweak: Exit with message instead of a panic

In case no application is found in GOPATH(s), exit with a friendly
message instead of a panic. Also removed useless else block in watch.go.

watch.go

@@ -240,9 +240,8 @@ func shouldIgnoreFile(filename string) bool {
 		}
 		if r.MatchString(filename) {
 			return true
-		} else {
-			continue
 		}
+		continue
 	}
 	return false
 }