Add PR templates and update install.sha256

.github/PULL_REQUEST_TEMPLATE.md

+# Description
+
+Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.
+
+Fixes # (issue)
+
+**Environment report**
+
+<!--
+Run the command `omf doctor` and paste the output here. Example:
+-->
+
+```
+Oh My Fish version:   6
+OS type:              Linux
+Fish version:         fish, version 2.7.1
+Git version:          git version 2.17.1
+Git core.autocrlf:    no
+Your shell is ready to swim.
+```
+
+# Checklist:
+
+- [ ] My code follows the [style guidelines](https://github.com/oh-my-fish/oh-my-fish/blob/master/CONTRIBUTING.md#code-style) of this project
+- [ ] I have performed a self-review of my own code
+- [ ] I have commented my code, particularly in hard-to-understand areas
+- [ ] I have made corresponding changes to the documentation
+- [ ] New and existing tests pass locally with my changes <!--
+remove next checkbox if you didn't change the install script -->
+- [ ] I have updated the SHA256 checksum for the install script

bin/install.sha256

-434264c56e3a7bb74733d9b293d72403c404e0a0bded3e632433d391d302504e  install
+bbace7ef16956d87fd40bff91cd1992a90621e7931ac3055f16b7f6d679e8fff  install

tests/run.fish

@@ -4,13 +4,23 @@
 
 set -l return_code 0
 
+omf list | grep apt 2>&1 >/dev/null
+set -l apt_installed_previously $status
+
+if test $apt_installed_previously -eq 0
+  omf remove apt
+end
+
 set commands "omf help" "omf doctor" "omf install apt"
 for cmd in $commands
   echo \$ $cmd
   if not eval $cmd
     set return_code 1
-  end;
-end;
+  end
+end
 
+if test $apt_installed_previously -ne 0
+  omf remove apt
+end
 
 exit $return_code