Bump Xcode project compatibility version

CryptoSwift.xcodeproj/project.pbxproj

@@ -761,7 +761,7 @@
 				};
 			};
 			buildConfigurationList = 754BE44F19693E190098E6F3 /* Build configuration list for PBXProject "CryptoSwift" */;
-			compatibilityVersion = "Xcode 8.0";
+			compatibilityVersion = "Xcode 9.3";
 			developmentRegion = en;
 			hasScannedForEncodings = 0;
 			knownRegions = (