Update structopt, base64, zip, serde_json, reqwest, flate2, byteorder

Update to structopt 0.3.15, closes #330
Update to base64 0.12.2, closes #329
Update to zip 0.5.6, closes #328
Update to serde_json 1.0.55, closes #327
Update to reqwest 0.10.6, closes #321
Update to flate2 1.0.14, closes #303
Update to byteorder 1.3.4, closes #285

Author: iceiix