Fiddle fails to run on Ubuntu

I have probably the same problem as #1598 when running the default fiddle. The AppArmor setting did not help.

Here is the error message:
```
Saving files to temp directory...
Saved files to /tmp/electron-fiddle-277819-LBRTE2pLL1zA
Electron v39.0.0 started.
LaunchProcess: failed to execvp:
/home/phi1010/.config/Electron
[279265:1108/112053.613267:FATAL:content/browser/zygote_host/zygote_host_impl_linux.cc:207] Check failed: . : Invalid argument (22)

Electron exited with signal SIGTRAP.
```

As far as I can see, fiddle attempts to run `/home/phi1010/.config/Electron` (which does not exist), while really, it should run `/home/phi1010/.config/Electron\ Fiddle/...`. There seems to be missing escaping/quoting of the space in the default config path.