travis: disable cache again to test build time

.travis.yml

@@ -2,7 +2,8 @@ language: rust
 
 # Caching of the runtime .wasm blob poses a problem.
 # See: https://github.com/Joystream/joystream/issues/466
-cache: cargo
+# Testing removing caching again on build time..
+# cache: cargo
 
 rust:
   - 1.43.0