zippy: Re-release snappy 1.1.5 as 1.1.6.

The migration from autotools to CMake in 1.1.5 wasn't as smooth as
intended. The SONAME / SOVERSION were broken in both build systems,
causing breakages in systems that upgraded from snappy 1.1.4 to 1.1.5,
as reported in https://github.com/Homebrew/homebrew-core/issues/15274
and https://github.com/google/snappy/pull/45.

CMakeLists.txt

@@ -1,5 +1,5 @@
 CMAKE_MINIMUM_REQUIRED(VERSION 3.1)
-PROJECT(Snappy VERSION 1.1.5 LANGUAGES C CXX)
+PROJECT(Snappy VERSION 1.1.6 LANGUAGES C CXX)
 
 SET(CMAKE_INCLUDE_CURRENT_DIR ON)
 
@@ -107,7 +107,8 @@ INSTALL(TARGETS snappy
         ARCHIVE DESTINATION lib)
 INSTALL(EXPORT SnappyTargets NAMESPACE Snappy:: DESTINATION lib/cmake/Snappy)
 
-SET_TARGET_PROPERTIES(snappy PROPERTIES SOVERSION ${PROJECT_VERSION})
+SET_TARGET_PROPERTIES(snappy PROPERTIES VERSION ${PROJECT_VERSION}
+                      SOVERSION ${PROJECT_VERSION_MAJOR})
 
 SET(INCLUDE_INSTALL_DIR include)
 SET(LIBRARY_INSTALL_DIR lib)