Update http package dependency

[cachapa]

The http update to 1.0.0 is breaking dependencies all over the place, including firebase_admin:

Because no versions of firebase_admin match >0.2.0 <0.3.0 and firebase_admin 0.2.0 depends on http ^0.13.0, firebase_admin ^0.2.0 requires http ^0.13.0.
So, because firedart depends on both http ^1.0.0 and firebase_admin ^0.2.0, version solving failed.

grpc-dart solved the problem by specifying a version window: http: '>=0.13.0 <2.0.0'
https://github.com/grpc/grpc-dart/pull/629/files