force:data:tree:export fails if username contains a whitespace

### Summary

_force:data:tree:export fails if the username contains a space_.

### Steps To Reproduce:

1. Have a Windows user where the username contains a whitespace (e.g. Time Lord)
1. Run this command `sfdx force:data:tree:export -q "SELECT Name, Location__Latitude__s, Location__Longitude__s FROM Account WHERE Location__Latitude__s != NULL AND Location__Longitude__s != NULL" -d ./data`

### Expected result

_This should export the data defined by the query_.

### Actual result

> 'C:\Users\Time' is not recognized as an internal or external command,
operable program or batch file.

### Additional information


**SFDX CLI Version**
sfdx-cli/6.55.1-be0b3dc4c4 (windows-x64) node-v8.9.4

**SFDX plugin Version**
@salesforce/plugin-generator 1.0.1 (core)
@salesforce/sfdx-trust 2.0.1 (core)
builtins 1.0.0 (core)
salesforcedx 45.4.1 (core)

**OS and version**:
Microsoft Windows [Version 10.0.17134.590]