AppVeyor breaks on linux builds

[nils-a]

The error is:

> Resolve dependencies of :idea
FAILURE: Build failed with an exception.
* What went wrong:
Could not determine the dependencies of task ':buildSearchableOptions'.
> Could not resolve all files for configuration ':detachedConfiguration3'.
   > Could not resolve com.jetbrains.intellij.rider:riderRD:2019.3.
     Required by:
         project :
      > Could not resolve com.jetbrains.intellij.rider:riderRD:2019.3.
         > Could not get resource 'https://cache-redirector.jetbrains.com/www.jetbrains.com/intellij-repository/releases/com/jetbrains/intellij/rider/riderRD/2019.3/riderRD-2019.3.pom'.
            > Could not GET 'https://cache-redirector.jetbrains.com/www.jetbrains.com/intellij-repository/releases/com/jetbrains/intellij/rider/riderRD/2019.3/riderRD-2019.3.pom'.
               > sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

Java config was:

========================================
Print-Java-Environment-Variables
========================================
Executing task: Print-Java-Environment-Variables
  JAVA_HOME: /usr/lib/jvm/java-10-openjdk-amd64/
  JAVA_OPTS: [NULL]
GRADLE_OPTS: [NULL]
Resolved tool to path /usr/lib/jvm/java-10-openjdk-amd64//bin/java
Java found at: /usr/lib/jvm/java-10-openjdk-amd64//bin/java
Executing: /usr/lib/jvm/java-10-openjdk-amd64//bin/java -version
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF8
openjdk version "10" 2018-03-20
OpenJDK Runtime Environment 18.3 (build 10+44)
OpenJDK 64-Bit Server VM 18.3 (build 10+44, mixed mode)
Finished executing task: Print-Java-Environment-Variables