Add missing space after "Serialized" in StorageLevel

Current code creates outputs like:

scala> res0.getStorageLevel.description
res2: String = Serialized1x Replicated
Typo: applicaton
Merge pull request #226 from ash211/patch-4

Typo: applicaton
Merge pull request #225 from ash211/patch-3

Add missing space after "Serialized" in StorageLevel

Current code creates outputs like:

scala> res0.getStorageLevel.description
res2: String = Serialized1x Replicated