Change date format to correct YYYY-MM-DD (#23)

Changed 2018-3-2 to 2018-03-02

Author: jrbell19

rest-example.py

@@ -5,7 +5,7 @@ def main():
     key = "your api key"
     client = RESTClient(key)
 
-    resp = client.stocks_equities_daily_open_close("AAPL", "2018-3-2")
+    resp = client.stocks_equities_daily_open_close("AAPL", "2018-03-02")
     print(f"On: {resp.from_} Apple opened at {resp.open} and closed at {resp.close}")