Update docs and scripts for v1.9.1 release

Author: borsboom

.github/ISSUE_TEMPLATE/bug_report.md

@@ -5,7 +5,7 @@ about: Report a bug in Stack
 
 Please follow the steps below for reporting a bug:
 
-Make sure that you are using the latest release (currently stack-1.7.1).
+Make sure that you are using the latest release (currently stack-1.9.1).
 See the [upgrade instructions](http://docs.haskellstack.org/en/stable/install_and_upgrade/#upgrade) to upgrade.
 
 Please use the following schema for your bug report:

.github/ISSUE_TEMPLATE/feature_request.md

@@ -3,7 +3,7 @@ name: Feature Request
 about: Request a feature be added to Stack, or discuss such a feature
 ---
 
-Make sure that you are using the latest release (currently stack-1.7.1).
+Make sure that you are using the latest release (currently stack-1.9.1).
 See the [upgrade instructions](http://docs.haskellstack.org/en/stable/install_and_upgrade/#upgrade) to upgrade.
 
 Please state as clearly as possible what feature you are recommending,

.github/ISSUE_TEMPLATE/question.md

@@ -9,7 +9,7 @@ This way your question will be more easily discoverable by other people with the
 
 Question related to stack project templates? Please report it at the [stack-templates](https://github.com/commercialhaskell/stack-templates) repository instead.
 
-if you still want to ask the question here instead, please make sure that you are using the latest release (current stack-1.7.1).
+if you still want to ask the question here instead, please make sure that you are using the latest release (current stack-1.9.1).
 See the [upgrade instructions](http://docs.haskellstack.org/en/stable/install_and_upgrade/#upgrade) to upgrade.
 
 ### Stack version

doc/yaml_configuration.md

@@ -887,7 +887,7 @@ Sets the address of the Hackage server to upload the package to. Default is
 hackage-base-url: https://hackage.example.com/
 ```
 
-Since 1.8.0
+Since 1.9.1
 
 ### ignore-revision-mismatch
 

etc/scripts/get-stack.sh

@@ -19,7 +19,7 @@
 # https://github.com/commercialhaskell/stack/blob/master/etc/scripts/get-stack.sh
 #
 
-STACK_VERSION="1.7.1"
+STACK_VERSION="1.9.1"
 HOME_LOCAL_BIN="$HOME/.local/bin"
 DEFAULT_DEST="/usr/local/bin/stack"
 DEST=""