Compose: ERROR: In file 'docker-compose.yml', service 'version' must be a mapping not a string.

[enriquecatala]

Description of the issue

After updating to docker-compose version 1.20.1, build 5d8c71b2, my docker-compose.yml file start crashing

Context information (for bug reports)

docker-compose version 1.20.1, build 5d8c71b2

```
Output of "docker version"
Docker version 18.03.0-ce, build 0520e24

Output of "docker-compose config"
PS D:Docker> docker-compose config
ERROR: In file '.docker-compose.yml', service 'version' must be a mapping not a string.

## Steps to reproduce the issue

1. Create the following docker-compose.yml file:
```yaml
version: '3'
services:
  mssql-server-linux:
    container_name: sql2017_flex_powerbi    
    image: microsoft/mssql-server-linux:latest
    volumes:
      - mssql-server-linux-data:/var/opt/mssql/data
    environment:
      MSSQL_SA_PASSWORD: "P@ssW0rd"
      ACCEPT_EULA: "Y"
    ports:
      - "14333:1433"

volumes:
  mssql-server-linux-data:

1. execute docker-compose config

Observed result

ERROR: In file '.\docker-compose.yml', service 'version' must be a mapping not a string.

Expected result

Create and run the new image

Stacktrace / full error message

ERROR: In file '.\docker-compose.yml', service 'version' must be a mapping not a string.

Additional information

OS version / distribution, docker-compose install method, etc.
I´m runing docker on Windows 10 Pro Version 1709 (os compilation 16299.309)

[shin-]

You have an encoding problem of some kind. Is your file using a BOM by any chance?

Try recreating the file with a different text editor.