[Fluid] Use correct char for colon

Closes: #265

Author: cedricziel

lang-fluid/src/main/grammars/FluidParser.bnf

@@ -18,7 +18,7 @@
     EXPR_START='{'
     EXPR_END='}'
 
-    COLON=','
+    COLON=':'
     DOT='.'
     COMMA=','
     ARROW='->'