put_timestamp_file.function bug

[RobertWan91]

Describe the bug
At line 985 in client.py (function: put_timestamp_file()):
if self.client.pachd_version >= '1.8.6'

if the version is 1.9.5, the above if is right.

But if the version is 1.10.5 or 1.11.1, the above if will give a False where a True should be generated.

To Reproduce
Steps to reproduce the behavior:
If pachyderm 1.10.5 is used, client.trigger_pipeline() function won't work properly

Environment:

• OS: macOS
• Python Version: 3.6.7
• Pachyderm Version: 1.10.5

Additional context
Add any other context about the problem here.