Add some missing keywords for mdBook syntax highlighting (FuelLabs#2903)

Add some missing keywords to the `sway.js` file. This was triggered by
@Braqzen noticing some inconsistent highlighting in the generated MD
books.

Doesn't address custom types not being highlighted but that can be for a
future PR.

docs/theme/highlight.js

@@ -303,8 +303,8 @@ anyNumberOfTimes:g};for(const e in A)"object"==typeof A[e]&&n(A[e])
 grmr_sway:e=>{const t={className:"title.function.invoke",relevance:0,
 begin:b(/\b/,/(?!let\b)/,e.IDENT_RE,u(/\s*\(/))},n="([u](8|16|32|64))?";return{
 name:"Sway",aliases:["sw"],keywords:{$pattern:e.IDENT_RE+"!?",
-keyword:["abi","as","asm","const","contract","deref","enum","fn","if","impl","let","library","match","mut","else","predicate","ref","return","script","Self","self","storage","str","struct","trait","use","where","while"],
-literal:["true","false"],
+keyword:["abi","as","asm","break","const","continue","contract","dep","deref","else","enum","fn","for","if","impl","let","library","match","mut","predicate","pub","ref","return","script","Self","self","storage","str","struct","trait","use","where","while"],
+literal:["true","false","Some","None","Ok","Err"],
 built_in:["bool","char","u8","u16","u32","u64","b256","str","Self"]},
 illegal:"</",contains:[e.C_LINE_COMMENT_MODE,e.COMMENT("/\\*","\\*/",{
 contains:["self"]}),e.inherit(e.QUOTE_STRING_MODE,{begin:/b?"/,illegal:null}),{

scripts/highlightjs/sway.js

@@ -25,19 +25,24 @@ export default function(hljs) {
     "abi",
     "as",
     "asm",
+    "break",
     "const",
+    "continue",
     "contract",
+    "dep",
     "deref",
+    "else",
     "enum",
     "fn",
+    "for",
     "if",
     "impl",
     "let",
     "library",
     "match",
     "mut",
-    "else",
     "predicate",
+    "pub",
     "ref",
     "return",
     "script",
@@ -54,6 +59,10 @@ export default function(hljs) {
   const LITERALS = [
     "true",
     "false",
+    "Some",
+    "None",
+    "Ok",
+    "Err",
   ];
   const BUILTINS = [