Updated doctest's output to reflect error message found in summer 2019.

• When running doctest for parse('invalid'):
  • error message encountered during lesson prep for soft 162 was different than error message in doctest
  • changed doctest to reflect current error message
• Possible discussion point for future is that error messages may change in future versions of Python, causing false-failures of tests

examples.py

@@ -11,7 +11,7 @@ def parse(pair):
     >>> parse('invalid')
     Traceback (most recent call last):
       ...
-    ValueError: need more than 1 value to unpack
+    ValueError: not enough values to unpack (expected 2, got 1)
 
     Likewise if there is more than one separator:
     >>> parse('first: second: third')