use a recent sbt-extras

fixes #765

Author: SethTisue

travis/default.yml

@@ -13,6 +13,12 @@ before_install:
     if [[ $ADOPTOPENJDK == 8 ]]; then versionPrefix="1\.8"; else versionPrefix=$ADOPTOPENJDK; fi
     java -version
   - java -version 2>&1 | grep 'AdoptOpenJDK.*[^0-9]'$versionPrefix'[^0-9]' || exit 1
+  # Travis-CI has (as of March 2021, anyway) an outdated sbt-extras version,
+  # so overwrite it with a March 2021 version that works with sbt 1.4.8+
+  - |
+    curl -sL https://raw.githubusercontent.com/paulp/sbt-extras/dc4f350f112580fcdf5f6fa7e8d5d2116475f84a/sbt  > /tmp/sbt-launch-script
+    chmod +x /tmp/sbt-launch-script
+    sudo mv /tmp/sbt-launch-script /usr/local/bin/sbt
 
 before_cache:
   - rm -fv $HOME/.ivy2/.sbt.ivy.lock