release/v2.26.0: updating version numbers

Author: serban-nicusor-toptal

.github/ISSUE_TEMPLATE.md

@@ -24,4 +24,4 @@ Describe what you expect the output to be. Knowing the correct behavior is also
 Provide any additional information here.
 
 #### Current Version:
-v2.25.0
+v2.26.0

makefile

@@ -130,7 +130,7 @@ include make/program
 include make/tests
 include make/command
 
-CMDSTAN_VERSION := 2.25.0
+CMDSTAN_VERSION := 2.26.0
 
 ifeq ($(OS),Windows_NT)
 HELP_MAKE=mingw32-make