Error starting reason-vscode "expected string", fix error message for invalid bsconfig.json

[MarcCoquand]

When trying to start vscode-reason I get the following error

Failure("Error \"Expected string\" at 8:3 -> \n")Raised at file "stdlib.ml", line 33, characters 17-33 
Called from file "vendor/Json.re", line 505, characters 28-55 Called from file "vendor/Json.re", line 505, 
characters 28-55 Called from file "vendor/Json.re", line 505, characters 28-55 Called from file 
"vendor/Json.re", line 520, characters 25-52 Called from file "vendor/Json.re", line 528, characters 
20-41 Called from file "src/analyze/Packages.re", line 49, characters 15-30 Called from file "src/analyze
/Packages.re", line 542, characters 24-73 Called from file "src/lsp/NotificationHandlers.re", line 74, 
characters 24-75 Called from file "src/lsp/BasicServer.re", line 84, characters 11-35

[MarcCoquand]

The error was thrown because I had an invalid bsconfig. The error message should be that the bsconfig is invalid.