Replace pkg_resources with importlib (#462)

poetry.lock

@@ -1868,4 +1868,4 @@ compiler = ["black", "isort", "jinja2"]
 [metadata]
 lock-version = "2.0"
 python-versions = "^3.7"
-content-hash = "f9503e42026d0807dc3ed344b5f8e6fa3f1c7ffa9c66b086de929aefaa8cb8c6"
+content-hash = "58b357685be67e8852b589ee0df3011b37dc1a2460ece732c0fa4c922f62bddd"

pyproject.toml

@@ -15,6 +15,7 @@ packages = [
 python = "^3.7"
 black = { version = ">=19.3b0", optional = true }
 grpclib = "^0.4.1"
+importlib-metadata = { version = ">=1.6.0", python = "<3.8" }
 jinja2 = { version = ">=3.0.3", optional = true }
 python-dateutil = "^2.8"
 isort = {version = "^5.11.5", optional = true}

src/betterproto/_version.py

@@ -1,4 +1,7 @@
-from pkg_resources import get_distribution
+try:
+    from importlib import metadata
+except ImportError:  # for Python<3.8
+    import importlib_metadata as metadata  # type: ignore
 
 
-__version__ = get_distribution("betterproto").version
+__version__ = metadata.version("betterproto")