Design doc: fix indent in the receivers config example (#447)
Design doc: fix indent in the receivers config example (#447)

- fix double quote in config examples
- remove some trailing white spaces and duplicate word

Signed-off-by: Hui Kang <06099befa36bf5a07a5196d8e1177abdf1d958ba@us.ibm.com>
open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector-contrib,open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector-contrib