⚗️ try to use GCC 10

.travis.yml

@@ -300,16 +300,6 @@ matrix:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-7']
         packages: ['g++-7', 'clang-7', 'ninja-build']
 
-  - os: linux
-    compiler: clang
-    env:
-      - COMPILER=clang++-7
-      - CXX_STANDARD=20
-    addons:
-      apt:
-        sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-7']
-        packages: ['g++-7', 'clang-7', 'ninja-build']
-
 ################
 # build script #
 ################