Update issue templates

Author: Weichen Shen

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Describe the bug(问题描述)**
+A clear and concise description of what the bug is.
+
+**To Reproduce(复现步骤)**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Operating environment(运行环境):**
+ - python version [e.g. 3.4, 3.6]
+ - tensorflow version [e.g. 1.4.0, 1.12.0]
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: enhancement&feature request
+assignees: ''
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/question.md

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+---
+name: Question
+about: Ask any question ~
+title: ''
+labels: question
+assignees: ''
+
+---
+
+**Describe the question(问题描述)**
+A clear and concise description of what the bug is.
+
+**Additional context**
+Add any other context about the problem here.