Timezone file not found at /usr/local/lib/python3.6/site-packages/pytzdata/zoneinfo/ #531
Description
In some special cases, for example, in a docker image which contains python environment "https://github.com/rappdw/docker-java-python", the method _get_unix_timezone in '/pendulum/tz/local_timezone.py' will result in an error like Timezone file not found at /usr/local/lib/python3.6/site-packages/pytzdata/zoneinfo/.
When "etc/timezone" exists, it may contains the tzinfo like "Asia/shanghai" where the first letter of shanghai is not capitalized, but the file names in /usr/local/lib/python3.6/site-packages/pytzdata/zoneinfo/ are all in the title case.
Because the part for reading "etc/timezone" is just before the part of reading "/etc/localtime", _get_unix_timezone will go to find a file like "Asia/shanghai" and the bug will come up.