Issue type:

[ ] bug report
[ ] feature request
[x] documentation issue

Database system/driver:

[ ] cordova
[ ] mongodb
[ ] mssql
[ ] mysql / mariadb
[ ] oracle
[x] postgres
[ ] cockroachdb
[ ] sqlite
[ ] sqljs
[ ] react-native
[ ] expo

TypeORM version:

[ ] latest
[ ] @next
[x] 0.2.25 (or put your version here)
but it still seems to be the case in the source code

Steps to reproduce or a small repository showing the problem:
I made a custom logger and followed the types provided by the library for logQueryError to take a first parameter error of type string, but when i actually inspect the error parameter it appears to be an instance of Error, not a string. This is misleading; are there certain cases where it will really be a string, or can the typing be changed entirely to Error or some subtype of Error?