fix

build_for_android.sh

@@ -7,7 +7,7 @@ cd $path
 cd ..
 git clone --depth=50 https://github.com/xiongziliang/ZLMediaKit.git
 cd ZLMediaKit
-git checkout 2.0-alpha
+git fetch origin 2.0-alpha:2.0-alpha
 mkdir -p android_build
 rm -rf ./build
 ln -s ./android_build build

build_for_linux.sh

@@ -13,7 +13,7 @@ cd $path
 cd ..
 git clone --depth=50 https://github.com/xiongziliang/ZLMediaKit.git
 cd ZLMediaKit
-git checkout 2.0-alpha
+git fetch origin 2.0-alpha:2.0-alpha
 mkdir -p linux_build
 rm -rf ./build
 ln -s ./linux_build build

build_for_mac.sh

@@ -12,7 +12,7 @@ cd $path
 cd ..
 git clone --depth=50 https://github.com/xiongziliang/ZLMediaKit.git
 cd ZLMediaKit
-git checkout 2.0-alpha
+git fetch origin 2.0-alpha:2.0-alpha
 mkdir -p mac_build
 rm -rf ./build
 ln -s ./mac_build build