Gets the module name of a given path.

e.g. `eslint/lib/ast-utils` -> `eslint`

@param {string} nameOrPath - A path to get.
@returns {string} The module name of the path.
function getModuleName(nameOrPath) {
    let end = nameOrPath.indexOf("/")
    if (end !== -1 && nameOrPath[0] === "@") {
        end = nameOrPath.indexOf("/", 1 + end)
    }

    return end === -1 ? nameOrPath : nameOrPath.slice(0, end)
}