Updating to latest ycmd

Also required an ABI version bump (some internal names were changed).

python/ycm/base.py

@@ -171,7 +171,7 @@ def OverlapLength( left_string, right_string ):
       length += 1
 
 
-COMPATIBLE_WITH_CORE_VERSION = 12
+COMPATIBLE_WITH_CORE_VERSION = 13
 
 def CompatibleWithYcmCore():
   try:

third_party/ycmd

@@ -1 +1 @@
-Subproject commit d27023566174b2864204f721faff2e0acd1efbb2
+Subproject commit 6b05f41434c8e0a28c5db3cfe909f6ec3d19d85e