fix(lib): fixing the feature confitional compilation

[vincenzopalazzo]

If you are installing coffee with make install you will receive the following error

   Compiling git2 v0.16.1
   Compiling coffee_lib v0.1.0 (/home/vincent/Github/coffee/coffee/coffee_lib)
error[E0433]: failed to resolve: use of undeclared crate or module `paperclip`
 --> coffee_lib/src/types/mod.rs:5:9
  |
5 |     use paperclip::actix::Apiv2Schema;
  |         ^^^^^^^^^ use of undeclared crate or module `paperclip`

error: cannot determine resolution for the derive macro `Apiv2Schema`
 --> coffee_lib/src/types/mod.rs:8:34
  |
8 |     #[derive(Debug, Deserialize, Apiv2Schema, Serialize)]
  |                                  ^^^^^^^^^^^
  |
  = note: import resolution is stuck, try simplifying macro imports

error: cannot determine resolution for the derive macro `Apiv2Schema`
  --> coffee_lib/src/types/mod.rs:14:34
   |
14 |     #[derive(Debug, Deserialize, Apiv2Schema, Serialize)]
   |                                  ^^^^^^^^^^^
   |
   = note: import resolution is stuck, try simplifying macro imports

error: cannot determine resolution for the derive macro `Apiv2Schema`
  --> coffee_lib/src/types/mod.rs:19:34
   |
19 |     #[derive(Debug, Deserialize, Apiv2Schema, Serialize)]
   |                                  ^^^^^^^^^^^
   |
   = note: import resolution is stuck, try simplifying macro imports

error: cannot determine resolution for the derive macro `Apiv2Schema`
  --> coffee_lib/src/types/mod.rs:25:34
   |
25 |     #[derive(Debug, Deserialize, Apiv2Schema, Serialize)]
   |                                  ^^^^^^^^^^^
   |
   = note: import resolution is stuck, try simplifying macro imports

error: cannot determine resolution for the derive macro `Apiv2Schema`
  --> coffee_lib/src/types/mod.rs:30:34
   |
30 |     #[derive(Debug, Deserialize, Apiv2Schema, Serialize)]
   |                                  ^^^^^^^^^^^
   |
   = note: import resolution is stuck, try simplifying macro imports

For more information about this error, try `rustc --explain E0433`.
error: could not compile `coffee_lib` (lib) due to 6 previous errors
warning: build failed, waiting for other jobs to finish...
error: failed to compile `coffee v0.0.1-alpha.1 (/home/vincent/Github/coffee/coffee/coffee_cmd)`, intermediate artifacts can be found at `/home/vincent/Github/coffee/coffee/target`.
To reuse those artifacts with a future compilation, set the environment variable `CARGO_TARGET_DIR` to that path.

This commit fix the confitional compilation

Fixes: 57b218d
Link #157

cc @tareknaser360

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