fix: FQCN highlighting of Jinja2 filters (pearofducks#138)

Fixes pearofducks#124

Author: sscheib

syntax/jinja2.vim

@@ -27,7 +27,7 @@ syn keyword jinjaSpecial containedin=jinjaVarBlock,jinjaTagBlock,jinjaNested con
 
 " Filters
 syn match jinjaOperator "|" containedin=jinjaVarBlock,jinjaTagBlock,jinjaNested contained skipwhite nextgroup=jinjaFilter
-syn match jinjaFilter contained /[a-zA-Z_][a-zA-Z0-9_]*/
+syn match jinjaFilter contained /[a-zA-Z_.][a-zA-Z0-9_.]*/
 syn match jinjaFunction contained /[a-zA-Z_][a-zA-Z0-9_]*/
 syn match jinjaBlockName contained /[a-zA-Z_][a-zA-Z0-9_]*/