[docs] change config version to v1

[tejal29]

Change config version to v1 everywhere in docs.

Before

tejaldesai@@skaffold1 (rename_config_version)$ grep -r 'skaffold\/v1' docs/
docs/content/en/samples/builders/custom-buildpacks/skaffold.yaml:apiVersion: skaffold/v1beta13

docs/content/en/docs/design/api.md:{"result":{"timestamp":"2019-10-16T18:26:11.385251549Z","event":
{"metaEvent":{"entry":"Starting Skaffold: {Version:v0.39.0-16-g5bb7c9e0 
ConfigVersion:skaffold/v1beta15
GitVersion: GitCommit:5bb7c9e078e4d522a5ffc42a2f1274fd17d75902 GitTreeState:dirty BuildDate:2019-10-03T15:01:29Z GoVersion:go1.13rc1 Compiler:gc Platform:linux/amd64}"}}}}

docs/content/en/docs/pipeline-stages/init.md:apiVersion: skaffold/v1beta15

docs/config.toml:skaffold_version = "skaffold/v1beta18"

After

tejaldesai@@skaffold1 (rename_config_version)$ grep -r 'skaffold\/v1' docs/
docs/content/en/samples/builders/custom-buildpacks/skaffold.yaml:apiVersion: skaffold/v1

docs/content/en/docs/design/api.md:{"result":{"timestamp":"2019-10-16T18:26:11.385251549Z","event":
{"metaEvent":{"entry":"Starting Skaffold: {Version:v0.39.0-16-g5bb7c9e0 
ConfigVersion:skaffold/v1 
GitVersion: GitCommit:5bb7c9e078e4d522a5ffc42a2f1274fd17d75902 GitTreeState:dirty BuildDate:2019-10-03T15:01:29Z GoVersion:go1.13rc1 Compiler:gc Platform:linux/amd64}"}}}}

docs/content/en/docs/pipeline-stages/init.md:apiVersion: skaffold/v1

docs/config.toml:skaffold_version = "skaffold/v1beta18"

[container-tools-bot]

Please visit http://35.235.117.222:1313 to view changes to the docs.

[codecov]

Codecov Report

Merging #3175 into master will not change coverage.
The diff coverage is n/a.