Fix Program node's sourceType.
Fix Program node's sourceType.

Somehow this was mistakenly introduced during the TypeScript migration.

Refs #1159
Closes gh-1372

ChromeDevTools/esprima,ariya/esprima,ChromeDevTools/esprima,jquery/esprima,bcbcarl/esprima,jquery/esprima,jquery/esprima,ChromeDevTools/esprima,bcbcarl/esprima,ariya/esprima,ariya/esprima,bcbcarl/esprima