For maths snippets, use $0 as the placeholder for the body part

This is related to James-Yu#609.

Author: jlelong

data/commands.json

@@ -1,22 +1,22 @@
 {
   "begin":{
     "command":"begin",
-    "snippet":"begin{${1:env}}\n\t$2\n\\\\end{${1:env}}",
+    "snippet":"begin{${1:env}}\n\t$0\n\\\\end{${1:env}}",
     "detail":"begin a new environment"
   },
   "lrparen":{
     "command":"left(",
-    "snippet":"left(${1}\\right)${0}",
+    "snippet":"left($0\\right)",
     "detail":"\\left( ... \\right)"
   },
   "lrbrack":{
     "command":"left[",
-    "snippet":"left[${1}\\right]${0}",
+    "snippet":"left[$0\\right]",
     "detail":"\\left[ ... \\right]"
   },
   "lrcurly":{
     "command":"left\\{",
-    "snippet":"left\\{${1}\\right\\\\}${0}",
+    "snippet":"left\\{$0\\right\\\\}",
     "detail":"\\left\\{ ... \\right\\}"
   },
   "frame": {
@@ -26,17 +26,17 @@
   },
   "latexinlinemath":{
     "command":"(",
-    "snippet":"(${1}\\)${0}",
+    "snippet":"(${0}\\)",
     "detail":"inline math \\( ... \\)"
   },
   "latexdisplaymath":{
     "command":"[",
-    "snippet":"[${1}\\]${0}",
+    "snippet":"[$0\\]",
     "detail":"display math \\[ ... \\]"
   },
   "curlybrackets":{
     "command":"{",
-    "snippet":"{${1}\\\\}${0}",
+    "snippet":"{$0\\\\}",
     "detail":"curly brackets \\{ ... \\}"
   },
   "title":{