[DocsetBuilder] Fix writing plist on older ruby versions
[DocsetBuilder] Fix writing plist on older ruby versions

realm/jazzy,realm/jazzy,agentk/jazzy,PSPDFKit-labs/jazzy,PSPDFKit-labs/jazzy,jeeftor/jazzy,Kapeli/jazzy,johndpope/jazzy,pcantrell/jazzy,emiscience/jazzy,agentk/jazzy,emiscience/jazzy,AliSoftware/jazzy,1ec5/jazzy,Kapeli/jazzy,1ec5/jazzy,mbogh/jazzy,johndpope/jazzy,AliSoftware/jazzy,pcantrell/jazzy,jeeftor/jazzy,AliSoftware/jazzy,pcantrell/jazzy,agentk/jazzy,jeeftor/jazzy,Kapeli/jazzy,mbogh/jazzy,johndpope/jazzy,emiscience/jazzy,mbogh/jazzy,1ec5/jazzy