Tighten install_requirements for deps

I skipped voluptuous as it is on 0.x.y and it isn't clear how a
breaking change would be versioned.

Author: oschwald

HISTORY.rst

@@ -8,6 +8,8 @@ History
 
 * Added ``py.typed`` file per PEP 561. Reported by Árni Már Jónsson. GitHub
   #62.
+* Tightened ``install_requirements`` for dependencies to prevent a new
+  major version from being installed.
 
 2.0.2 (2020-07-27)
 ++++++++++++++++++

setup.py

@@ -17,11 +17,11 @@
     _readme = f.read()
 
 requirements = [
-    "aiohttp>=3.6.2",
-    "email_validator",
+    "aiohttp>=3.6.2,<4.0.0",
+    "email_validator>=1.1.1,<2.0.0",
     "geoip2>=4.0.0,<5.0.0",
-    "requests>=2.24.0",
-    "urllib3>=1.25.2",
+    "requests>=2.24.0,<3.0.0",
+    "urllib3>=1.25.2,<2.0.0",
     "voluptuous",
 ]