fix python version (coolsnowwolf#3352)

an@ubuntu:~/lede$ ./scripts/feeds update -a
Updating feed 'packages' from 'https://github.com/coolsnowwolf/packages' ...
Already up-to-date.
Create index file './feeds/packages.index' 
Checking 'working-make'... ok.
Checking 'case-sensitive-fs'... ok.
Checking 'proper-umask'... ok.
Checking 'gcc'... ok.
Checking 'working-gcc'... ok.
Checking 'g++'... ok.
Checking 'working-g++'... ok.
Checking 'ncurses'... ok.
Checking 'perl-thread-queue'... ok.
Checking 'tar'... ok.
Checking 'find'... ok.
Checking 'bash'... ok.
Checking 'patch'... ok.
Checking 'diff'... ok.
Checking 'cp'... ok.
Checking 'seq'... ok.
Checking 'awk'... ok.
Checking 'grep'... ok.
Checking 'getopt'... ok.
Checking 'stat'... ok.
Checking 'unzip'... ok.
Checking 'bzip2'... ok.
Checking 'wget'... ok.
Checking 'perl'... ok.
Checking 'python2-cleanup'... ok.
Checking 'python'... failed.
Checking 'python3'... failed.
Checking 'git'... ok.
Checking 'file'... ok.
Checking 'ldconfig-stub'... ok.

Build dependency: Please install Python >= 3.5
Build dependency: Please install Python >= 3.5

Prerequisite check failed. Use FORCE=1 to override.
make: *** [staging_dir/host/.prereq-build] Error 1

README

@@ -12,7 +12,7 @@
 1. 首先装好 Ubuntu 64bit，推荐  Ubuntu  14 LTS x64
 
 2. 命令行输入 sudo apt-get update ，然后输入
-sudo apt-get -y install build-essential asciidoc binutils bzip2 gawk gettext git libncurses5-dev libz-dev patch python3 unzip zlib1g-dev lib32gcc1 libc6-dev-i386 subversion flex uglifyjs git-core gcc-multilib p7zip p7zip-full msmtp libssl-dev texinfo libglib2.0-dev xmlto qemu-utils upx libelf-dev autoconf automake libtool autopoint device-tree-compiler g++-multilib linux-libc-dev:i386
+sudo apt-get -y install build-essential asciidoc binutils bzip2 gawk gettext git libncurses5-dev libz-dev patch python3.5 unzip zlib1g-dev lib32gcc1 libc6-dev-i386 subversion flex uglifyjs git-core gcc-multilib p7zip p7zip-full msmtp libssl-dev texinfo libglib2.0-dev xmlto qemu-utils upx libelf-dev autoconf automake libtool autopoint device-tree-compiler g++-multilib linux-libc-dev:i386
 
 3. git clone https://github.com/coolsnowwolf/lede 命令下载好源代码，然后 cd lede 进入目录