Updated README.md to use scala-js 1.3.0

Author: cheeseng

README.md

@@ -29,7 +29,7 @@ Please use the following commands to publish to Sonatype:
 ```
 $ export SCALAJS_VERSION=0.6.33
 $ sbt clean +scalatestPlusScalaCheckJS/publishSigned +scalatestPlusScalaCheckJVM/publishSigned scalatestPlusScalaCheckNative/publishSigned
-$ export SCALAJS_VERSION=1.2.0
+$ export SCALAJS_VERSION=1.3.0
 $ sbt ++2.11.12 "project scalatestPlusScalaCheckJS" clean publishSigned
 $ sbt ++2.12.12 "project scalatestPlusScalaCheckJS" clean publishSigned
 $ sbt ++2.13.3 "project scalatestPlusScalaCheckJS" clean publishSigned