chore: improve assert descriptions in crowdfund.vy (vyperlang#3064)

---------

Co-authored-by: Charles Cooper <cooper.charles.m@gmail.com>
Co-authored-by: El De-dog-lo <3859395+fubuloubu@users.noreply.github.com>

examples/crowdfund.vy

@@ -18,15 +18,15 @@ def __init__(_beneficiary: address, _goal: uint256, _timelimit: uint256):
 @external
 @payable
 def participate():
-    assert block.timestamp < self.deadline, "deadline not met (yet)"
+    assert block.timestamp < self.deadline, "deadline has expired"
 
     self.funders[msg.sender] += msg.value
 
 # Enough money was raised! Send funds to the beneficiary
 @external
 def finalize():
-    assert block.timestamp >= self.deadline, "deadline has passed"
-    assert self.balance >= self.goal, "the goal has not been reached"
+    assert block.timestamp >= self.deadline, "deadline has not expired yet"
+    assert self.balance >= self.goal, "goal has not been reached"
 
     selfdestruct(self.beneficiary)