update stable release version in install doc (#361)

Author: Brian969

docs/installation/index.md

@@ -153,7 +153,7 @@ If deploying to an internal AWS account, to successfully install the entire solu
    - you must supply this bucket name in the CFN parameters _and_ in the config file
    - the bucket name _must_ be the same in both spots
    - the bucket should be `S3-KMS` encrypted using either the `AwsLandingZoneKMSKey` or the `Accel-Source-Bucket-Key` created above
-5. Place your customized config file, named `config.json` (or `config/yaml`), in your new bucket
+5. Place your customized config file, named `config.json` (or `config.yaml`), in your new bucket
 6. Place the firewall configuration and license files in the folder and path defined in the config file
    - i.e. `firewall/firewall-example.txt`, `firewall/license1.lic` and `firewall/license2.lic`
    - Sample available here: `./reference-artifacts/Third-Party/firewall-example.txt`
@@ -179,7 +179,7 @@ If deploying to an internal AWS account, to successfully install the entire solu
 8. Add an `Email` address to be used for State Machine Status notification
 9. The `GithubBranch` should point to the release you selected
    - if upgrading, change it to point to the desired release
-   - the latest stable branch is currently `release/v1.1.7`, case sensitive
+   - the latest stable branch is currently `release/v1.1.8`, case sensitive
 10. Apply a tag on the stack, Key=`Accelerator`, Value=`PBMM` (case sensitive).
 11. **ENABLE STACK TERMINATION PROTECTION** under `Stack creation options`
 12. The stack typically takes under 5 minutes to deploy.