Fix string type for buildargs API definition

Signed-off-by: Jon Surrell <jon.surrell@gmail.com>

api/swagger.yaml

@@ -6174,7 +6174,7 @@ paths:
         - name: "buildargs"
           in: "query"
           description: "JSON map of string pairs for build-time variables. Users pass these values at build-time. Docker uses the buildargs as the environment context for commands run via the `Dockerfile` RUN instruction, or for variable expansion in other `Dockerfile` instructions. This is not meant for passing secret values. [Read more about the buildargs instruction.](https://docs.docker.com/engine/reference/builder/#arg)"
-          type: "integer"
+          type: "string"
         - name: "shmsize"
           in: "query"
           description: "Size of `/dev/shm` in bytes. The size must be greater than 0. If omitted the system uses 64MB."