Update issue templates

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Bug report issue template
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**OS**
+Operation system's name and version
+
+**Neovim version**
+output of `nvim --version`
+
+**Nvim-tree version**
+nvim-tree branch, commit or tag number
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.