ci: Switch coverage build from ninja to make

Author: chfast

circle.yml

@@ -251,7 +251,7 @@ jobs:
       - BUILD_TYPE: Debug
       - CXX: g++
       - CC:  gcc
-      - GENERATOR: Ninja
+      - GENERATOR: Unix Makefiles
       - BUILD_PARALLEL_JOBS: 4
       - CMAKE_OPTIONS: -DCOVERAGE=ON -DBUILD_SHARED_LIBS=ON -DHERA_DEBUGGING=ON -DHERA_BINARYEN=ON -DHERA_WABT=ON -DHERA_WAVM=ON
       - TESTETH_OPTIONS: --evmc benchmark=true