[Build] Switch from xctool to xcodebuild to work around Travis image …

…bugs

The output is far less readable, but it seems much more reliable.  See:
travis-ci/travis-ci#3986

build.sh

@@ -20,7 +20,7 @@ MODE="$1"
 if [ "$MODE" = "tests" ]; then
     echo "Building & testing AsyncDisplayKit."
     pod install
-    xctool \
+    xcodebuild \
         -workspace AsyncDisplayKit.xcworkspace \
         -scheme AsyncDisplayKit \
         -sdk "$SDK" \
@@ -40,7 +40,7 @@ if [ "$MODE" = "examples" ]; then
           echo "Using CocoaPods"
           pod install --project-directory=$example
 
-          xctool \
+          xcodebuild \
               -workspace "${example}Sample.xcworkspace" \
               -scheme Sample \
               -sdk "$SDK" \
@@ -55,7 +55,7 @@ if [ "$MODE" = "examples" ]; then
           echo "git \"file://${local_repo}\" \"${current_branch}\"" > "Cartfile"
           carthage update --platform iOS
 
-          xctool \
+          xcodebuild \
               -project "Sample.xcodeproj" \
               -scheme Sample \
               -sdk "$SDK" \
@@ -72,7 +72,7 @@ fi
 if [ "$MODE" = "life-without-cocoapods" ]; then
     echo "Verifying that AsyncDisplayKit functions as a static library."
 
-    xctool \
+    xcodebuild \
         -workspace "smoke-tests/Life Without CocoaPods/Life Without CocoaPods.xcworkspace" \
         -scheme "Life Without CocoaPods" \
         -sdk "$SDK" \
@@ -85,7 +85,7 @@ fi
 if [ "$MODE" = "framework" ]; then
     echo "Verifying that AsyncDisplayKit functions as a dynamic framework (for Swift/Carthage users)."
 
-    xctool \
+    xcodebuild \
         -project "smoke-tests/Framework/Sample.xcodeproj" \
         -scheme Sample \
         -sdk "$SDK" \