German adjectives ending on `-e` are not lemmatized using the lookup lemmatizer

## How to reproduce the behaviour

import spacy
nlp = spacy.load('de')
s1 = 'Der schöne Garten'
doc = nlp(s1)
[(t, t.lemma_) for t in doc]
>> [(Der, 'der'), (schöne, 'schöne'), (Garten, 'Garten')]

s2 = 'Ein schöner Garten'
doc = nlp(s2)
[(t, t.lemma_) for t in doc]
>> [(Ein, 'Ein'), (schöner, 'schön'), (Garten, 'Garten')]

## My Environment

* **spaCy version:** 2.2.2
* **Platform:** Linux-5.0.0-25-generic-x86_64-with-LinuxMint-19.2-tina
* **Python version:** 3.6.7
* **Models:** de

## Reason

As far as I can see, all forms of German adjectives ending on `e` in `spacy-lookups-data/spacy_lookups_data/data/de_lemma_lookup.json` are capitalized, e.g.:

"Dekorative": "dekorativ",
"Weiße": "Weiß",
"Schöne": "Schönes",