Bundlewatch throws an exception if there is no package.json in the current directory.

[rogersd]

Do you want to request a feature or report a bug?

Bug report.

What is the current behavior?

Bundlewatch throws an exception if there is no package.json in the current directory, even when passing --config

If the current behavior is a bug, please provide the steps to reproduce.

1. From a directory with no package.json, run /usr/local/bin/npx bundlewatch --config foo.json. The following exception will occur:

TypeError: Cannot read property 'bundlewatch' of undefined
    at determineConfig (/Users/drogers/.npm/_npx/3805/lib/node_modules/bundlewatch/lib/bin/determineConfig.js:70:36)
    at main (/Users/drogers/.npm/_npx/3805/lib/node_modules/bundlewatch/lib/bin/index.js:51:47)
    at mainSafe (/Users/drogers/.npm/_npx/3805/lib/node_modules/bundlewatch/lib/bin/index.js:102:29)
    at Object.<anonymous> (/Users/drogers/.npm/_npx/3805/lib/node_modules/bundlewatch/lib/bin/index.js:149:1)
    at Module._compile (internal/modules/cjs/loader.js:1251:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1272:10)
    at Module.load (internal/modules/cjs/loader.js:1100:32)
    at Function.Module._load (internal/modules/cjs/loader.js:962:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at /usr/local/lib/node_modules/npm/node_modules/libnpx/index.js:268:14
[FATAL] Uncaught exception

What is the expected behavior?

The missing package.json should be ignored, and the proviced config file used.

If this is a feature request, what is motivation or use case for changing the behavior?

Please mention other relevant information such as the browser version, Node.js version, bundlewatch version, and Operating System.