Update issue templates

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Bug report
+
+---
+
+Operating system(s):
+Version of Rack if using official binary, or commit hash and branch if compiling from source:

.github/ISSUE_TEMPLATE/discussion.md

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+---
+name: Discussion
+about: Discussion
+
+---
+
+

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Feature request
+
+---
+
+