build: update CMake minimum version to 3.1

In scope of implementing self-sufficient testing environment LuaJIT
build system is partially ported to CMake. While integrating the new
build system with Tarantool it was found (on practice of course) that
using generator expressions[1] in target DEPENDS section is introduced
only in CMake 3.1[2]. This CMake feature is used to pass so called
"LuaJIT binary" to be used in LuaJIT tests, so one can run the same
testing machinery with both Tarantool and LuaJIT with no changes in it.

[1]: https://cmake.org/cmake/help/v3.1/manual/cmake-generator-expressions.7.html
[2]: https://cmake.org/cmake/help/latest/release/3.1.html#commands



Relates to #4862

Reviewed-by: Alexander V. Tikhonov <avtikhon@tarantool.org>
Signed-off-by: Igor Munkin <imun@tarantool.org>

@TarantoolBot document
Title: Update CMake minimum required version in build documentation

This commit updates the CMake minimum required version to be used in
Tarantool build infrastructure. However, one can build Tarantool from
sources and the required toolchain list should be updated. CMake minimum
required version is 3.1 since this commit. See the commit message for
more info.