Remove leading "$ " from copy-pastable commands (dependabot#20)

When showing both the command and logs, the leading dollar makes things
more readable. However, in snippets with individual commands it doesn't
make it look better, and it's more useful without since it makes the
command directly pasted in the terminal work.

Author: deivid-rodriguez

README.md

@@ -103,7 +103,7 @@ using the `--file` / `-f` option
 (this replaces the package manager and repository name arguments).
 
 ```console
-$ dependabot update -f job.yaml --dry-run
+dependabot update -f job.yaml --dry-run
 ```
 
 ```yaml
@@ -265,14 +265,14 @@ To produce a scenario file that tests Dependabot behavior for a given repo,
 run the `update` subcommand and set the `--output` / `-o` option to a file path.
 
 ```console
-$ dependabot update go_modules rsc/quote --dry-run -o go-scenario.yml
+dependabot update go_modules rsc/quote --dry-run -o go-scenario.yml
 ```
 
 Run the `test` subcommand for the generated scenario file,
 specifying a cache directory with the `--cache` option.
 
 ```console
-$ dependabot test -f go-scenario.yml --cache ./tmp/cache
+dependabot test -f go-scenario.yml --cache ./tmp/cache
 ```
 
 While performing the update job,
@@ -310,7 +310,7 @@ to get the latest version of Docker installed and running.
 You can verify that Docker is running locally with the following command:
 
 ```console
-$ docker --version
+docker --version
 ```
 
 ### "Network internet is ambiguous"
@@ -324,7 +324,7 @@ This error can occur when the CLI exits before having an opportunity to clean up
 Run the following command to remove all unused networks:
 
 ```console
-$ docker network prune
+docker network prune
 ```
 
 [Docker]: https://docs.docker.com/get-started/