add CommandContext as subprocess launcher

rules/subproc.go

@@ -58,6 +58,7 @@ func (r *subprocess) Match(n ast.Node, c *gas.Context) (*gas.Issue, error) {
 func NewSubproc(id string, conf gas.Config) (gas.Rule, []ast.Node) {
 	rule := &subprocess{gas.MetaData{ID: id}, gas.NewCallList()}
 	rule.Add("os/exec", "Command")
+	rule.Add("os/exec", "CommandContext")
 	rule.Add("syscall", "Exec")
 	return rule, []ast.Node{(*ast.CallExpr)(nil)}
 }

testutils/source.go

@@ -408,6 +408,20 @@ func main() {
   	log.Printf("Command finished with error: %v", err)
 }`, 1}, {`
 package main
+import (
+	"log"
+	"os/exec"
+	"context"
+)
+func main() {
+	err := exec.CommandContext(context.Background(), "sleep", "5").Run()
+ 	if err != nil {
+		log.Fatal(err)
+	}
+  	log.Printf("Command finished with error: %v", err)
+}
+}`, 1}, {`
+package main
 import (
 	"log"
 	"os"