Add package to CI script.

.github/workflows/ci.yml

@@ -69,7 +69,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        compiler: [ g++-9, g++-10 ]
+        compiler: [ g++ ]
         standard: [ c++11, c++14, c++17, c++2a ]
     steps:
       - uses: actions/checkout@v2
@@ -85,7 +85,7 @@ jobs:
       - name: Add repository
         run: sudo apt-add-repository -y "ppa:ubuntu-toolchain-r/test"
       - name: Install packages
-        run: sudo apt install g++-9 g++-10
+        run: sudo apt install libicu-dev
       - name: Test
         run: ${{ matrix.compiler }} -std=${{ matrix.standard }}  -I../../include *.cpp ../../src/*.cpp -o regress -licuuc -licui18n && ./regress
         working-directory: ./test/regress