Auto merge of #2902 - micbou:update-ycmd, r=puremourning

[READY] Update ycmd

Include the following changes:

 - PR ycm-core/ycmd#789: add support for Windows flags when --driver-mode=cl is given;
 - PR ycm-core/ycmd#848: hide C++ symbols by default;
 - PR ycm-core/ycmd#857: add Java support using jdt.ls;
 - PR ycm-core/ycmd#861: translate libclang error codes to exceptions;
 - PR ycm-core/ycmd#880: support downloading Clang binaries on ARM systems;
 - PR ycm-core/ycmd#883: handle zero column diagnostic from OmniSharp;
 - PR ycm-core/ycmd#884: specify Platform property when compiling OmniSharp;
 - PR ycm-core/ycmd#886: use current working directory in JavaScript completer;
 - PR ycm-core/ycmd#887: update Boost to 1.66.0;
 - PR ycm-core/ycmd#888: update JediHTTP;
 - PR ycm-core/ycmd#889: update Clang to 5.0.1;
 - PR ycm-core/ycmd#891: fix building with system libclang on Gentoo amd64;
 - PR ycm-core/ycmd#904: drop Python 2.6 and Python 3.3 support;
 - PR ycm-core/ycmd#905: calculate the start column when items are not resolved in the language server completer;
 - PR ycm-core/ycmd#912: download Clang binaries from HTTPS;
 - PR ycm-core/ycmd#914: do not try to symlink libclang on Windows.

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