Upgrade dependencies and update used JDKs (tus#16)

* Remove unsupported JDK versions

* Update Gradle to version 4.4

* Disable ECDSA algorithm

* Run before install

* Fix deprication error for left shift operator

The error in question was:
> The Task.leftShift(Closure) method has been deprecated and is scheduled to be
> removed in Gradle 5.0. Please use Task.doLast(Action) instead.

* Remove Java 6 tests but compile with support for Java 6

Gradle has problem downloading dependencies:
https://travis-ci.org/tus/tus-java-client/jobs/318341024#L505

* Update mockserver-netty

* Use sudo for changing Java security file

* Add comment

Deployment support for jdk 6 (tus#12)

0.3.1

This small release only contains one patch will cause a new upload
to be automatically be created when using the `TusClient#resumeOrCreateUpload`
method and if the original upload cannot be found anymore since the tus server
sends back the `404 Not Found` status code (see tus#3).

This minor release contains some pretty neat features mostly focusing

on a better uploading experience:

* Added `TusExecutor` for automatic retries and resumes
* Added `@NotNull` and `@Nullable` annotations for some methods
* Added `TusClient#setHeaders` for custom headers in requests
* Added filename into metadata by default
* Added `Expect: 100-continue` header for faster error handling

* Test response header's values for not being null before accessing t…

…heir length

  to prevent NullPointerException.

This minor release adds the TusUploader#setChunkSize() and

TusUploader#uploadChunk() methods while deprecating the original
TusUploader#uploadChunk(int) method in order to reduce memory
allocations by resuing internal buffers.

Add dependecy for example project

Use pomVersion for variable in Gradle

Fix deployment to Bintray

Use mocking server for Creation responses