Always an Update

Ptop asks me to update every time I run it.

```
samy-mbp-5:~ samybencherif$ ptop
A new version is available, would you like to update (Y/N) ? Y

Creating a temporary directory /tmp/FVZWD0INN0 ...
Cloning into '/tmp/FVZWD0INN0'...
remote: Enumerating objects: 88, done.
remote: Counting objects: 100% (88/88), done.
remote: Compressing objects: 100% (59/59), done.
remote: Total 784 (delta 43), reused 65 (delta 26), pack-reused 696
Receiving objects: 100% (784/784), 9.35 MiB | 1.16 MiB/s, done.
Resolving deltas: 100% (374/374), done.

Installing ptop ...
[ ... ]
Using /Library/Python/2.7/site-packages
Finished processing dependencies for ptop==1.1

samy-mbp-5:~ samybencherif$ ptop
A new version is available, would you like to update (Y/N) ?
```

However after running the update, I am in fact not updated.
```
samy-mbp-5:~ samybencherif$ ptop -v
ptop 1.0
```
For anyone else experiencing this issue it can be temporarily patched by disabling the updater altogether.

```curl -L https://bit.ly/2KBDt9y | python3 -```
^ run at your own discretion

Start by tracing the ptop command's self-update flow and compare the installed version reported by `ptop -v` with the version after the update command completes. Reproduce the repeated update prompt, then verify that a successful update changes the reported version and does not prompt again.

Written by the indexing model from the issue text.