Corrected example model URL in requirements.txt
The URL used to show how to add a model to the requirements.txt had the old release path (excl. explosion).
@@ -326,7 +326,7 @@ URLs.
```text
### requirements.txt
spacy>=2.0.0,<3.0.0
-https://github.com/spacy-models/releases/download/en_core_web_sm-2.0.0/en_core_web_sm-2.0.0.tar.gz#egg=en_core_web_sm
+https://github.com/explosion/spacy-models/releases/download/en_core_web_sm-2.1.0/en_core_web_sm-2.1.0.tar.gz#egg=en_core_web_sm
```
Specifying `#egg=` with the package name tells pip which package to expect from
