chore: add missing type extension dependency (#75)

Author: Noah

requirements.in

@@ -10,4 +10,5 @@ py-githooks
 pytest
 semver
 twine
+typing_extensions
 wheel

requirements.txt

@@ -53,7 +53,7 @@ toml==0.10.0              # via black, coverage
 tqdm==4.41.0              # via twine
 twine==3.1.1
 typed-ast==1.4.0          # via black, mypy
-typing-extensions==3.7.4.1  # via mypy
+typing-extensions==3.7.4.1
 urllib3==1.25.7           # via requests
 wcwidth==0.1.7            # via pytest
 webencodings==0.5.1       # via bleach

setup.py

@@ -38,7 +38,7 @@ def readme() -> str:
         package_dir={"": "src"},
         packages=find_packages("./src"),
         zip_safe=False,
-        install_requires=[],
+        install_requires=["typing_extensions"],
         setup_requires=["setuptools_scm"],
         entry_points={"pytest11": ["syrupy = syrupy"]},
         python_requires=python_requires,