Fix doxygen check (#149)

* Update doxygen version

* update the config file

Author: AniruddhaKanhere

.github/workflows/ci.yml

@@ -97,7 +97,7 @@ jobs:
       - uses: actions/checkout@v2
       - name: Install Doxygen
         run: |
-          wget -qO- "http://doxygen.nl/files/doxygen-1.8.20.linux.bin.tar.gz" | sudo tar --strip-components=1 -xz -C /usr/local
+          wget -qO- "http://doxygen.nl/files/doxygen-1.9.1.linux.bin.tar.gz" | sudo tar --strip-components=1 -xz -C /usr/local
           sudo apt-get install -y libclang-9-dev
       - name: Run Doxygen And Verify Stdout Is Empty
         run: |