Add echo_hub, asr_hub and tts_hub demos.

demos/asr_hub/run.sh

 #!/bin/bash
 
+if python -c "import paddlehub" &> /dev/null; then
+    echo 'PaddleHub has already been installed.'
+else
+    echo 'Installing PaddleHub...'
+    pip install paddlehub -U
+fi
+
 mkdir -p data
 wav_en=data/en.wav
 wav_zh=data/zh.wav

demos/echo_hub/run.sh

 #!/bin/bash
 
+if python -c "import paddlehub" &> /dev/null; then
+    echo 'PaddleHub has already been installed.'
+else
+    echo 'Installing PaddleHub...'
+    pip install paddlehub -U
+fi
+
 if [ $# != 2 -a $# != 3 ];then
     echo "usage: CUDA_VISIBLE_DEVICES=0 ${0} text output_dir [lang]"
     exit -1

demos/tts_hub/run.sh

 #!/bin/bash
 
+if python -c "import paddlehub" &> /dev/null; then
+    echo 'PaddleHub has already been installed.'
+else
+    echo 'Installing PaddleHub...'
+    pip install paddlehub -U
+fi
+
 if [ $# != 2 -a $# != 3 ];then
     echo "usage: CUDA_VISIBLE_DEVICES=0 ${0} text output_dir [lang]"
     exit -1