Fixes typos in Migration15.md (#1717)
Fixes typos in Migration15.md (#1717)

(same as #1696, but for Scala documentation)
rcavalcanti/lagom,lagom/lagom,rstento/lagom,TimMoore/lagom,rstento/lagom,ignasi35/lagom,lagom/lagom,rstento/lagom,lagom/lagom,TimMoore/lagom,rstento/lagom,ignasi35/lagom,ignasi35/lagom,TimMoore/lagom,rstento/lagom,rcavalcanti/lagom,rcavalcanti/lagom,rcavalcanti/lagom,ignasi35/lagom,TimMoore/lagom,TimMoore/lagom,lagom/lagom,ignasi35/lagom,lagom/lagom