Get require expression module id

@inner
@param {Object} node the require call expression node
@param {Object} t the bable type definition
@return {?string}
function getRequireExpressionModuleId(node, t) {
    if (t.isCallExpression(node)) {
        let {arguments: args, callee} = node;
        if (t.isIdentifier(callee)
            && callee.name === 'require'
            && args.length === 1
            && t.isLiteral(args[0])
        ) {
            let id = args[0].value;
            return id;
        }
    }
}