bump multidict dependency version to 4.7.3

Author: chrissimpkins

requirements.txt

@@ -13,7 +13,7 @@ cffi==1.13.2              # via pycares
 chardet==3.0.4            # via aiohttp
 fonttools==4.2.2
 idna==2.8                 # via yarl
-multidict==4.7.1          # via aiohttp, yarl
+multidict==4.7.3          # via aiohttp, yarl
 pycares==3.1.0            # via aiodns
 pycparser==2.19           # via cffi
 yarl==1.4.2               # via aiohttp