Feature/Upgrade http dependency version

[sebasbad]

Issue

Incompatible combination of dependencies:

image_picker: ^0.7.1
gallery_saver: ^2.0.3

Because gallery_saver >=1.0.0 depends on http ^0.12.0+2 and image_picker_platform_interface >=2.0.0 depends on http ^0.13.0, gallery_saver >=1.0.0 is incompatible with image_picker_platform_interface >=2.0.0.
And because image_picker >=0.7.0 depends on image_picker_platform_interface ^2.0.0, gallery_saver >=1.0.0 is incompatible with image_picker >=0.7.0.

Proposed solution

Upgrade the http dependency from http: ^0.12.0+2 to http: ^0.13.0.