Description
Invocations that timeout are not being recorded in 1.7.18 - If there is no timeout, the invocation shows up in the dashboard

Steps to reproduce the issue:
Installing via pip with latest 1.7.18 - No invocation record recorded on a timeout

mkdir test
cd test
mkdir package
cd package/
pip install iopipe --target .
zip -r9 ../function.zip .
cd ../
zip -g function.zip function.py
aws lambda update-function-code --function-name timeout-support-2 --zip-file fileb://function.zip

Removing 1.7.18 and Installing 1.7.17 - Invocation timeout recorded in dashboard

cd package/
rm -rf *
pip install iopipe==1.7.17 -t .
zip -r9 ../function.zip .
cd ../
zip -g function.zip function.py
aws lambda update-function-code --function-name timeout-support-2 --zip-file fileb://function.zip

Additional information you deem important (e.g. issue happens only occasionally):
Set a time.sleep(6) in the code on a function with a three second timeout.