fix sql query for create user

[ardani]

i try on my computer it doesn't work,
i found the query was generate by code is wrong so i push my fix to make sql user generate work well

[lauriejim]

The generated request does't work with postgres now.
``` is not recognized by postgres. In fact you just have to make a condition like this line https://github.com/strapi/strapi/pull/497/files#diff-0c0ec60e7cc771f905ecac28620fe70fR286 to apply " if necessary.

[Aurelsicoko]

The PR (#507) also introduces new changes concerning these lines.

[Aurelsicoko]

Thank you for this PR, we fixed it in another PR and it has been merged on master.