Fix typo

Bolean -> Boolean

PR-URL: #2210
Credit: @HollowMan6
Close: #2210
Reviewed-by: @nlf

Author: HollowMan6

docs/content/commands/npm-explain.md

@@ -56,7 +56,7 @@ node_modules/nyc/node_modules/find-up
 #### json
 
 * Default: false
-* Type: Bolean
+* Type: Boolean
 
 Show information in JSON format.