Use cargo run in the adapter

Makes it easier to start the app eliminating the danger of forgetting to
build.

adapter/adapter.py

@@ -15,9 +15,10 @@ HERE = os.path.abspath(os.path.dirname(__file__))
 app = flask.Flask(__name__)
 CORS(app)
 engine = subprocess.Popen(
-    [os.path.join(HERE, "../rs/target/debug/schach")],
+    ["cargo", "run"],
     stdin=subprocess.PIPE,
     stdout=subprocess.PIPE,
+    cwd=os.path.join(HERE, "../rs"),
 )