Fix restarting server in dev

Wait for the server process to exit before starting a new one, so that
the server debugger port is free when the new process begins.

src/api/dev.ts

@@ -267,14 +267,7 @@ class Watcher extends EventEmitter {
 							});
 					};
 
-					if (this.proc) {
-						this.proc.removeListener('exit', emitFatal);
-						this.proc.kill();
-						this.proc.on('exit', restart);
-					} else {
-						restart();
-					}
-
+					const start_server = () => {
 						// we need to give the child process its own DevTools port,
 						// otherwise Node will try to use the parent's (and fail)
 						const debugArgRegex = /--inspect(?:-brk|-port)?|--debug-port/;
@@ -309,6 +302,19 @@ class Watcher extends EventEmitter {
 						});
 
 						this.proc.on('exit', emitFatal);
+					};
+
+					if (this.proc) {
+						this.proc.removeListener('exit', emitFatal);
+						this.proc.kill();
+						this.proc.on('exit', () => {
+							start_server();
+							restart();
+						});
+					} else {
+						start_server();
+						restart();
+					}
 				});
 			}
 		});