Fix dynamic macOS Travis failure by updating the xcode image.

Author: evoskuil

.travis.yml

@@ -19,6 +19,7 @@ addons:
 matrix:
     include:
         - os: osx
+          osx_image: xcode12.2
           compiler: clang
           env: LINK=dynamic
         - os: osx
@@ -59,9 +60,6 @@ before_install:
     - if [[ $TRAVIS_OS_NAME == osx     ]]; then OSX=true; fi
     - if [[ $TRAVIS_OS_NAME == linux   ]]; then LINUX=true; fi
 
-    # Update homebrew.
-    - if [[ $OSX   && $CLANG && $DYNAMIC ]]; then brew update; fi
-
 install:
 
     # Export CC/CXX to control compiler/version.
@@ -86,7 +84,7 @@ script:
 
 after_success:
 
-    # Download and unpack lcov > 1.10
+    # Download and unpack lcov.
     - if [[ $LINUX && $GCC   && $STATIC  ]]; then wget https://github.com/linux-test-project/lcov/releases/download/v1.12/lcov-1.12.tar.gz; fi
     - if [[ $LINUX && $GCC   && $STATIC  ]]; then tar xzf lcov-1.12.tar.gz; fi
     - if [[ $LINUX && $GCC   && $STATIC  ]]; then cd lcov-1.12; PREFIX="$TRAVIS_BUILD_DIR/my-prefix" make install; cd ..; fi