Downgrade default swift version

Demo/Kingfisher-Demo.xcodeproj/project.pbxproj

@@ -896,7 +896,7 @@
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 4.2;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				TVOS_DEPLOYMENT_TARGET = 10.0;
 				WATCHOS_DEPLOYMENT_TARGET = 3.0;
@@ -947,7 +947,7 @@
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 4.2;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				TVOS_DEPLOYMENT_TARGET = 10.0;
 				VALIDATE_PRODUCT = YES;

Kingfisher.xcodeproj/project.pbxproj

@@ -1413,7 +1413,6 @@
 				SDKROOT = appletvos;
 				SWIFT_OBJC_BRIDGING_HEADER = "Tests/KingfisherTests/KingfisherTests-Bridging-Header.h";
 				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
-				SWIFT_VERSION = "";
 				TARGETED_DEVICE_FAMILY = 3;
 			};
 			name = Debug;
@@ -1433,7 +1432,6 @@
 				SWIFT_OBJC_BRIDGING_HEADER = "Tests/KingfisherTests/KingfisherTests-Bridging-Header.h";
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
 				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
-				SWIFT_VERSION = "";
 				TARGETED_DEVICE_FAMILY = 3;
 			};
 			name = Release;
@@ -1642,7 +1640,7 @@
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 4.2;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				TVOS_DEPLOYMENT_TARGET = 10.0;
 				WATCHOS_DEPLOYMENT_TARGET = 3.0;
@@ -1693,7 +1691,7 @@
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
-				SWIFT_VERSION = 5.0;
+				SWIFT_VERSION = 4.2;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				TVOS_DEPLOYMENT_TARGET = 10.0;
 				VALIDATE_PRODUCT = YES;
@@ -1767,7 +1765,6 @@
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SWIFT_OBJC_BRIDGING_HEADER = "Tests/KingfisherTests/KingfisherTests-Bridging-Header.h";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 5.0;
 			};
 			name = Debug;
 		};
@@ -1783,7 +1780,6 @@
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SWIFT_OBJC_BRIDGING_HEADER = "Tests/KingfisherTests/KingfisherTests-Bridging-Header.h";
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
-				SWIFT_VERSION = 5.0;
 			};
 			name = Release;
 		};