Bump iOS deployment target to 16.4

This is the minimum on Sketch iOS project and silences the warning
about iOS 11 not being supported by Xcode anymore.

Author: jpedroso

Bugsnag.xcodeproj/project.pbxproj

@@ -3285,7 +3285,7 @@
 				DYLIB_CURRENT_VERSION = 1;
 				DYLIB_INSTALL_NAME_BASE = "@rpath";
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
-				IPHONEOS_DEPLOYMENT_TARGET = 11.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 16.4;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
@@ -3310,7 +3310,7 @@
 				DYLIB_CURRENT_VERSION = 1;
 				DYLIB_INSTALL_NAME_BASE = "@rpath";
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
-				IPHONEOS_DEPLOYMENT_TARGET = 11.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 16.4;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",