can't conda update because phantom notebook server running

I couldn't update my Python 3 conda environment today and the `NotebookRunningError` messages indicated it was because a Jupyter notebook server was running. I had just booted up my machine within the last hour and had not launched a notebook server. I'm on a MBP running macOS Sierra.

Here's the result of my command line tests:

#### Checking what notebook servers are "running"
```
jupyter notebook list:
Currently running servers:
http://localhost:8888/ :: /Users/eseiver/anaconda3
http://localhost:8888/?token=[token] :: /Users/eseiver/PLOS_Corpus_Project
```
[also weird b/c I am using miniconda now not anaconda]

#### Checking if there is a background process in screen
```
screen -r:
There is no screen to be resumed.
```

#### Check all processes
1) Following https://github.com/jupyter/notebook/issues/1950#issuecomment-318512976
```
pgrep jupyter
```
no output i.e. no processes running with 'jupyter' in name
[though I understand this doesn't work on Macs?]
2) Grepping the process list directly
```
ps aux | grep jupyter:
eseiver 3144 0.0 0.0 2473332 4 s000 S 12:56PM 0:00.00 grep jupyter
```
[pretty sure this means it's only finding the grep process]
3) See which processes are listening on port 8888, based on [this SO post](https://unix.stackexchange.com/a/149478/140059)
```
lsof -Pi :8888 -sTCP:LISTEN
```
no output, i.e. port 8888 is not registering any activity

#### Check that it is accessible in browser
`http://localhost:8888/` tested in the browser; connection refused.

@mpacer @minrk @Carreau