doc: fix a/an article typos in module, util, and dns

Signed-off-by: Daijiro Wachi <daijiro.wachi@gmail.com>

Author: watilde

doc/api/dns.md

@@ -483,7 +483,7 @@ changes:
   * `err` {Error}
   * `addresses` {string\[] | Object\[]}
 
-Uses the DNS protocol to resolve a IPv4 addresses (`A` records) for the
+Uses the DNS protocol to resolve an IPv4 addresses (`A` records) for the
 `hostname`. The `addresses` argument passed to the `callback` function
 will contain an array of IPv4 addresses (e.g.
 `['74.125.79.104', '74.125.79.105', '74.125.79.106']`).

doc/api/module.md

@@ -534,7 +534,7 @@ For general use cases, it's recommended to call `module.enableCompileCache()` wi
 specifying the `options.directory`, so that the directory can be overridden by the
 `NODE_COMPILE_CACHE` environment variable when necessary.
 
-Since compile cache is supposed to be a optimization that is not mission critical, this
+Since compile cache is supposed to be an optimization that is not mission critical, this
 method is designed to not throw any exception when the compile cache cannot be enabled.
 Instead, it will return an object containing an error message in the `message` field to
 aid debugging. If compile cache is enabled successfully, the `directory` field in the

doc/api/util.md

@@ -1580,7 +1580,7 @@ symbol is [registered globally][global symbol registry] and can be
 accessed in any environment as `Symbol.for('nodejs.util.inspect.custom')`.
 
 Using this allows code to be written in a portable fashion, so that the custom
-inspect function is used in an Node.js environment and ignored in the browser.
+inspect function is used in a Node.js environment and ignored in the browser.
 The `util.inspect()` function itself is passed as third argument to the custom
 inspect function to allow further portability.