Support building with JDK 10 and 11

[l0s]

As mentioned in #10, the build fails with JDK 10 and higher. Travis CI supports JDK 10 and 11 so at minimum, those versions should be supported.

JDK 10, 12, 14 issue:

[INFO] --- maven-compiler-plugin:3.7.0:testCompile (default-testCompile) @ xsync ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 5 source files to /Users/cmacasaet/var/git/xsync/target/test-classes
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by lombok.javac.apt.LombokProcessor to field com.sun.tools.javac.processing.JavacProcessingEnvironment.discoveredProcs
WARNING: Please consider reporting this to the maintainers of lombok.javac.apt.LombokProcessor
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  5.028 s
[INFO] Finished at: 2020-10-03T18:57:34-07:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.7.0:testCompile (default-testCompile) on project xsync: Fatal error compiling: java.lang.ExceptionInInitializerError: com.sun.tools.javac.code.TypeTags -> [Help 1]