Fixed code example for medspacy

[w2o-hbrashear]

Fix code example error in docs for medspacy

Description

The medspacy code example does not work as written. I've added changes that fix the run errors.

Types of change

1. update pipe name from "target_matcher" to "medspacy_target_matcher"
2. update import for "visualize_ent"

Example code was tested on medspacy version '1.3.1'

Checklist

• [ x] I confirm that I have the right to submit this contribution under the project's MIT license.
• [ x] I ran the tests, and all new and existing tests passed.
• [ x] My changes don't require a change to the documentation, or if they do, I've added all required information.