Rename package srverrors to httperror

- Package names are preferred to be in singular form¹.
- Since errors are just for HTTP and not generic, I changed the base name to
'http'.
- I didn't name it simply 'error', because it would then conflict with the
- standard 'error' interface.

¹: https://rakyll.org/style-packages/

internal/server/data/decorator.go

@@ -19,8 +19,8 @@ package data
 import (
 	"net/http"
 
+	"github.com/BBVA/kapow/internal/server/httperror"
 	"github.com/BBVA/kapow/internal/server/model"
-	"github.com/BBVA/kapow/internal/server/srverrors"
 	"github.com/gorilla/mux"
 )
 
@@ -40,7 +40,7 @@ func checkHandler(fn resourceHandler) func(http.ResponseWriter, *http.Request) {
 		if h, ok := Handlers.Get(handlerID); ok {
 			fn(w, r, h)
 		} else {
-			srverrors.ErrorJSON(w, "Handler ID Not Found", http.StatusNotFound)
+			httperror.ErrorJSON(w, "Handler ID Not Found", http.StatusNotFound)
 		}
 	}
 }