feat: bump MACOSX_DEPLOYMENT_TARGET from 10.8 to new minimum 10.13 (#581)

Thanks!

I'm not too worried about keeping deployment_version synced with tests... since the tests are empty.

ios-deploy.xcodeproj/project.pbxproj

diff --git a/ios-deploy.xcodeproj/project.pbxproj b/ios-deploy.xcodeproj/project.pbxproj
index 2539f72..c87c44f 100644
--- a/ios-deploy.xcodeproj/project.pbxproj
+++ b/ios-deploy.xcodeproj/project.pbxproj
@@ -326,7 +326,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				MACOSX_DEPLOYMENT_TARGET = 10.8;
+				MACOSX_DEPLOYMENT_TARGET = 10.13;
 				MTL_ENABLE_DEBUG_INFO = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				OTHER_LDFLAGS = (
@@ -381,7 +381,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				MACOSX_DEPLOYMENT_TARGET = 10.8;
+				MACOSX_DEPLOYMENT_TARGET = 10.13;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				OTHER_LDFLAGS = (
 					"-framework",