doc: replace tabs with spaces for alignment in code snippets

Fixes #52255

Change-Id: Ibb518cf2f6bac9e1ffc426a014afe80cc4c0df5e
Reviewed-on: https://go-review.googlesource.com/c/go/+/399394
Reviewed-by: Jamal Carvalho <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>

Author: looshch

doc/go_spec.html

@@ -800,7 +800,7 @@ <h2 id="Types">Types</h2>
 TypeArgs  = "[" TypeList [ "," ] "]" .
 TypeList  = Type { "," Type } .
 TypeLit   = ArrayType | StructType | PointerType | FunctionType | InterfaceType |
-	    SliceType | MapType | ChannelType .
+            SliceType | MapType | ChannelType .
 </pre>
 
 <p>
@@ -3015,7 +3015,7 @@ <h3 id="Qualified_identifiers">Qualified identifiers</h3>
 </p>
 
 <pre>
-math.Sin	// denotes the Sin function in package math
+math.Sin // denotes the Sin function in package math
 </pre>
 
 <h3 id="Composite_literals">Composite literals</h3>
@@ -4841,7 +4841,7 @@ <h4 id="Integer_operators">Integer operators</h4>
 </p>
 
 <pre>
-			 x, q
+                         x, q
 int8                     -128
 int16                  -32768
 int32             -2147483648