spec: add missing space in EBNF

Fixes #36520

Change-Id: I698ab235f82f7c81caa09318c954847cf3833153
GitHub-Last-Rev: 368a1dc
GitHub-Pull-Request: #36559
Reviewed-on: https://go-review.googlesource.com/c/go/+/214821
Reviewed-by: Robert Griesemer <gri@golang.org>

doc/go_spec.html

@@ -1,6 +1,6 @@
 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of Jan 13, 2020",
+	"Subtitle": "Version of Jan 14, 2020",
 	"Path": "/ref/spec"
 }-->
 
@@ -2413,7 +2413,7 @@ <h3 id="Operands">Operands</h3>
 Operand     = Literal | OperandName | "(" Expression ")" .
 Literal     = BasicLit | CompositeLit | FunctionLit .
 BasicLit    = int_lit | float_lit | imaginary_lit | rune_lit | string_lit .
-OperandName = identifier | QualifiedIdent.
+OperandName = identifier | QualifiedIdent .
 </pre>
 
 <h3 id="Qualified_identifiers">Qualified identifiers</h3>