fix uppercase regex

@@ -2,4 +2,4 @@ this a template file
 
 var = [[{variable}]]
 
-otra_variable= [[{var}]]
\ No newline at end of file
+otra_variable= [[{VAR}]]
\ No newline at end of file

@@ -15,8 +15,8 @@ class MyTemplate(string.Template):
     pattern = r'''
     \[\[\{(?:
     (?P<escaped>\[\[\{)|
-    (?P<named>[_a-z][_a-z0-9]*)\}\]\]|
-    (?P<braced>[_a-z][_a-z0-9]*)\}\]\]|
+    (?P<named>[_A-Z][_A-Z0-9]*)\}\]\]|
+    (?P<braced>[_A-Z][_A-Z0-9]*)\}\]\]|
     (?P<invalid>)
     )
     '''