Improve markdown code style.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -12,11 +12,10 @@ labels: bug
 - [ ] There are no similar reports on existing issues (including closed ones).
 - [ ] I found the bug on the latest code of `master` branch.
 
-
 ## Describe the bug
 <!-- A clear and concise description of what the bug is. -->
 
-**To Reproduce**
+### To Reproduce
 
 Steps to reproduce the behavior:
 
@@ -25,25 +24,24 @@ Steps to reproduce the behavior:
 3. Scroll down to '....'
 4. See error
 
-
-**Expected behavior**
+### Expected behavior
 <!-- A clear and concise description of what you expected to happen. -->
 
-**Screenshots**
+### Screenshots
 <!-- If applicable, add screenshots to help explain your problem. -->
 
-**Desktop**
+### Desktop
 <!-- Please complete the following information -->
- - OS: [e.g. iOS]
- - Browser: [e.g. chrome, safari]
- - Version: [e.g. 22]
+- OS: [e.g. iOS]
+- Browser: [e.g. chrome, safari]
+- Version: [e.g. 22]
 
-**Smartphone**
+### Smartphone
 <!-- please complete the following information -->
- - Device: [e.g. iPhone6]
- - OS: [e.g. iOS8.1]
- - Browser: [e.g. stock browser, safari]
- - Version: [e.g. 22]
+- Device: [e.g. iPhone6]
+- OS: [e.g. iOS8.1]
+- Browser: [e.g. stock browser, safari]
+- Version: [e.g. 22]
 
-**Additional context**
+### Additional context
 <!-- Add any other context about the problem here. -->