[release] snippets: avoid using "var" as default name in snippets

"var" is a reserved keyword. Some snippets using "var" as the default name produce Error: "expected 1 expression"
Replace the usage with more general names like `v`

Fixes #969

Change-Id: If335db938715a7c79e72e7e4d2fd0dc87507ca1d
GitHub-Last-Rev: 835feb4
GitHub-Pull-Request: #970
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/273746
Reviewed-by: Suzy Mueller <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
Trust: Suzy Mueller <[email protected]>
Trust: Hyang-Ah Hana Kim <[email protected]>
(cherry picked from commit e8d462e)
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/276213
Run-TryBot: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: RomanKornev

snippets/go.json

@@ -67,7 +67,7 @@
 		},
 		"for range statement": {
 			"prefix": "forr",
-			"body": "for ${1:_, }${2:var} := range ${3:var} {\n\t$0\n}",
+			"body": "for ${1:_, }${2:v} := range ${3:v} {\n\t$0\n}",
 			"description": "Snippet for a for range loop"
 		},
 		"channel declaration": {