devd: Use the standard constructor of std::string instead of string("").

Submitted by:	Christoph Mallon <christoph.mallon@gmx.de>
Approved by:	cperciva (mentor)

sbin/devd/devd.hh

@@ -144,7 +144,7 @@ private:
 class config
 {
 public:
-	config() : _pidfile("") { push_var_table(); }
+	config() { push_var_table(); }
 	virtual ~config() { reset(); }
 	void add_attach(int, event_proc *);
 	void add_detach(int, event_proc *);