Remove duplicate URL from deprecation message and fix indentation (#48)

* Remove duplicate URL from deprecation message

Fixes the duplicate URL + long ling wrapping seen currently:

```
-----> Redis-stunnel app detected
! This buildpack uses stunnel, which isn’t supported on heroku-24 and later.
! You don’t need this buildpack for Redis 6+. Remove it with the command:
! $ heroku buildpacks:remove heroku/redis
! To use Redis’ native TLS support, see https://devcenter.heroku.com/articles/heroku-redis#security-and-compliance:
! https://devcenter.heroku.com/articles/heroku-redis#security-and-compliance
 !     Push rejected, failed to compile Redis-stunnel app.
```

* Update indentation to match style used elsewhere

The build system (and other buildpacks) indent one space further for warning messages.

This fixes the wonky indentation seen here compared to the last log line (which comes from the build system):

Before:

```
-----> Redis-stunnel app detected
! This buildpack uses stunnel, which isn’t supported on heroku-24 and later.
! You don’t need this buildpack for Redis 6+. Remove it with the command:
! $ heroku buildpacks:remove heroku/redis
! To use Redis’ native TLS support, see:
! https://devcenter.heroku.com/articles/heroku-redis#security-and-compliance
 !     Push rejected, failed to compile Redis-stunnel app.
```

After:

```
-----> Redis-stunnel app detected
 !     This buildpack uses stunnel, which isn’t supported on heroku-24 and later.
 !     You don’t need this buildpack for Redis 6+. Remove it with the command:
 !     $ heroku buildpacks:remove heroku/redis
 !     To use Redis’ native TLS support, see:
 !     https://devcenter.heroku.com/articles/heroku-redis#security-and-compliance
 !     Push rejected, failed to compile Redis-stunnel app.
```

bin/compile

@@ -15,11 +15,11 @@ BUILDPACK_DIR="$(dirname $(dirname $0))"
 
 if ! command -v stunnel4 > /dev/null; then
 
-    echo "! This buildpack uses stunnel, which isn’t supported on heroku-24 and later." >&2
-    echo "! You don’t need this buildpack for Redis 6+. Remove it with the command:" >&2
-    echo "! $ heroku buildpacks:remove heroku/redis" >&2
-    echo "! To use Redis’ native TLS support, see https://devcenter.heroku.com/articles/heroku-redis#security-and-compliance:" >&2
-    echo "! https://devcenter.heroku.com/articles/heroku-redis#security-and-compliance" >&2
+    echo " !     This buildpack uses stunnel, which isn’t supported on heroku-24 and later." >&2
+    echo " !     You don’t need this buildpack for Redis 6+. Remove it with the command:" >&2
+    echo " !     $ heroku buildpacks:remove heroku/redis" >&2
+    echo " !     To use Redis’ native TLS support, see:" >&2
+    echo " !     https://devcenter.heroku.com/articles/heroku-redis#security-and-compliance" >&2
 
     exit 1
 fi