fix typo error

doc/doc_ch/installation.md

@@ -58,7 +58,7 @@ git clone https://gitee.com/paddlepaddle/PaddleOCR
 **4. 安装第三方库**
 ```
 cd PaddleOCR
-pip3 install -r requirments.txt
+pip3 install -r requirements.txt
 ```
 
 注意，windows环境下，建议从[这里](https://www.lfd.uci.edu/~gohlke/pythonlibs/#shapely)下载shapely安装包完成安装，

doc/doc_ch/tree.md

@@ -211,6 +211,6 @@ PaddleOCR
 ├── README_ch.md                            // 中文说明文档
 ├── README_en.md                            // 英文说明文档
 ├── README.md                               // 主页说明文档
-├── requirments.txt                         // 安装依赖
+├── requirements.txt                         // 安装依赖
 ├── setup.py                                // whl包打包脚本
 ├── train.sh                                // 启动训练脚本

doc/doc_en/installation_en.md

@@ -61,7 +61,7 @@ git clone https://gitee.com/paddlepaddle/PaddleOCR
 **4. Install third-party libraries**
 ```
 cd PaddleOCR
-pip3 install -r requirments.txt
+pip3 install -r requirements.txt
 ```
 
 If you getting this error `OSError: [WinError 126] The specified module could not be found` when you install shapely on windows.

doc/doc_en/tree_en.md

@@ -214,6 +214,6 @@ PaddleOCR
 ├── README_ch.md                            // Chinese documentation
 ├── README_en.md                            // English documentation
 ├── README.md                               // Home page documentation
-├── requirments.txt                         // Requirments
+├── requirements.txt                         // Requirements
 ├── setup.py                                // Whl package packaging script
 ├── train.sh                                // Start training bash script