Warn against deleting .julia folder with deved packages. (#1061)

* Warn against deleting `.julia` folder with deved packages.

* Update docs/src/manual/troubleshooting.md

Co-authored-by: Steven G. Johnson <[email protected]>

---------

Co-authored-by: Viral B. Shah <[email protected]>
Co-authored-by: Steven G. Johnson <[email protected]>

Author: 3 people

docs/src/manual/troubleshooting.md

@@ -7,7 +7,7 @@
 problem you can type `Pkg.build()` to try to rerun the install scripts.
 * If you tried it a while ago, try running `Pkg.update()` and try again:
   this will fetch the latest versions of the Julia packages in case
-  the problem you saw was fixed.  Run `Pkg.build("IJulia")` if your Julia version may have changed.  If this doesn't work, you could try just deleting the whole `.julia` directory in your home directory (on Windows, it is called `Users\USERNAME\.julia` in your home directory) via `rm(Pkg.dir(),recursive=true)` in Julia and re-adding the packages.
+  the problem you saw was fixed.  Run `Pkg.build("IJulia")` if your Julia version may have changed.  If this doesn't work, you could try just deleting the whole `.julia/conda` directory in your home directory (on Windows, it is called `Users\USERNAME\.julia\conda` in your home directory) via `rm(abspath(first(DEPOT_PATH), "conda"),recursive=true)` in Julia and re-adding the packages. 
 * On MacOS, you currently need MacOS 10.7 or later; [MacOS 10.6 doesn't work](https://github.com/JuliaLang/julia/issues/4215) (unless you compile Julia yourself, from source code).
 * Internet Explorer 8 (the default in Windows 7) or 9 don't work with the notebook; use Firefox (6 or later) or Chrome (13 or later).  Internet Explorer 10 in Windows 8 works (albeit with a few rendering glitches), but Chrome or Firefox is better.
 * If the notebook opens up, but doesn't respond (the input label is `In[*]` indefinitely), try creating a new Python notebook (not Julia) from the `New` button in the Jupyter dashboard, to see if `1+1` works in Python.  If it is the same problem, then probably you have a [firewall running](https://github.com/ipython/ipython/issues/2499) on your machine (this is common on Windows) and you need to disable the firewall or at least to allow the IP address 127.0.0.1.  (For the [Sophos](https://en.wikipedia.org/wiki/Sophos) endpoint security software, go to "Configure Anti-Virus and HIPS", select "Authorization" and then "Websites", and add 127.0.0.1 to "Authorized websites"; finally, restart your computer.) If the Python test works, then IJulia may not be installed in the global or default environment and you may need to install a custom Julia kernel that uses your required `Project.toml` (see [Julia projects](@ref)).