Setup python_requires to >=3.6

Fix python_requires format

python_apps/airtime-celery/setup.py

@@ -18,6 +18,7 @@ setup(
     },
     license="MIT",
     packages=["airtime-celery"],
+    python_requires=">=3.6",
     install_requires=[
         "celery==4.4.7",
         "kombu==4.6.10",

python_apps/airtime_analyzer/setup.py

@@ -23,6 +23,7 @@ setup(
             "libretime-analyzer=airtime_analyzer.cli:main",
         ]
     },
+    python_requires=">=3.6",
     install_requires=[
         "mutagen>=1.31.0",
         "pika>=1.0.0",

python_apps/api_clients/setup.py

@@ -18,6 +18,7 @@ setup(
     },
     license="AGPLv3",
     packages=["api_clients"],
+    python_requires=">=3.6",
     install_requires=[
         "configobj",
         "python-dateutil>=2.7.0",

python_apps/pypo/setup.py

@@ -27,6 +27,7 @@ setup(
         "bin/airtime-liquidsoap",
         "bin/pyponotify",
     ],
+    python_requires=">=3.6",
     install_requires=[
         "amqplib",
         "configobj",