seed-react-app: fix tslint warn about variable names

[juanmait]

There are some tslint warnings about variable names that don't apply to react apps:

variable name must be in lowerCamelCase or UPPER_CASE (variable-name)

Installing tslint-react should fix this and other potential problems

It doesn't. but this rule will do the job

"rules": {
  "variable-name": [true, "allow-leading-underscore", "allow-pascal-case"],
 }