Update user_login method to submit form data as dictionary instead of str.format() (#72)

Author: kwshi

piazza_api/rpc.py

@@ -77,8 +77,14 @@ def user_login(self, email=None, password=None):
 
         # Log in using credentials and CSRF token and store cookie in session
         response = self.session.post(
-            'https://piazza.com/class', 
-            data=r'from=%2Fsignup&email={0}&password={1}&remember=on&csrf_token={2}'.format(email, password, csrf_token)
+            "https://piazza.com/class",
+            data={
+                "from": "/signup",
+                "email": email,
+                "password": password,
+                "remember": "on",
+                "csrf_token": csrf_token,
+            },
         )
 
         # If non-successful http response, bail