feat: update minimum CMake version to 3.5

Author: Lyokone

CMakeLists.txt

@@ -14,7 +14,7 @@
 
 # Top level CMake file that defines the entire Firebase C++ SDK build.
 
-cmake_minimum_required (VERSION 3.1)
+cmake_minimum_required (VERSION 3.5)
 
 set (CMAKE_CXX_STANDARD 14)
 set (CMAKE_CXX_STANDARD_REQUIRED YES)  # Don't fall back to an earlier version.

app/rest/CMakeLists.txt

@@ -14,7 +14,7 @@
 
 # CMake file for the firebase_rest_lib library
 
-cmake_minimum_required (VERSION 3.1)
+cmake_minimum_required (VERSION 3.5)
 # Firebase C++ SDK requires C++14.
 set (CMAKE_CXX_STANDARD 14)
 set (CMAKE_CXX_STANDARD_REQUIRED YES)  # Don't fall back to an earlier version.

ios_pod/empty_CMakeLists.txt

@@ -14,7 +14,7 @@
 
 # Stub cmake project to enable pod files to be installed against
 
-cmake_minimum_required (VERSION 3.1)
+cmake_minimum_required (VERSION 3.5)
 
 project (GetPods CXX)
 add_library(GetPods empty.cc)

release_build_files/CMakeLists.txt

@@ -14,7 +14,7 @@
 
 # Top level CMake file that defines targets for the Firebase C++ SDK.
 
-cmake_minimum_required(VERSION 3.1)
+cmake_minimum_required(VERSION 3.5)
 
 include(FindPkgConfig)
 

testing/CMakeLists.txt

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-cmake_minimum_required (VERSION 3.1)
+cmake_minimum_required (VERSION 3.5)
 set (CMAKE_CXX_STANDARD 14)
 set (CMAKE_CXX_STANDARD_REQUIRED YES)  # Don't fall back to an earlier version.