doc: remove redundant empty lines

doc/api/addons.md

@@ -217,7 +217,6 @@ Addon developers are recommended to use to keep compatibility between past and
 future releases of V8 and Node.js. See the `nan` [examples][] for an
 illustration of how it can be used.
 
-
 ## N-API
 
 > Stability: 1 - Experimental
@@ -307,7 +306,6 @@ built using `node-gyp`:
 $ node-gyp configure build
 ```
 
-
 ### Function arguments
 
 Addons will typically expose objects and functions that can be accessed from
@@ -381,7 +379,6 @@ const addon = require('./build/Release/addon');
 console.log('This should be eight:', addon.add(3, 5));
 ```
 
-
 ### Callbacks
 
 It is common practice within Addons to pass JavaScript functions to a C++
@@ -488,7 +485,6 @@ console.log(obj1.msg, obj2.msg);
 // Prints: 'hello world'
 ```
 
-
 ### Function factory
 
 Another common scenario is creating JavaScript functions that wrap C++
@@ -546,7 +542,6 @@ console.log(fn());
 // Prints: 'hello world'
 ```
 
-
 ### Wrapping C++ objects
 
 It is also possible to wrap C++ objects/classes in a way that allows new
@@ -916,7 +911,6 @@ console.log(obj2.plusOne());
 // Prints: 23
 ```
 
-
 ### Passing wrapped objects around
 
 In addition to wrapping and returning C++ objects, it is possible to pass

doc/api/async_hooks.md

@@ -141,7 +141,6 @@ future. This is subject to change in the future if a comprehensive analysis is
 performed to ensure an exception can follow the normal control flow without
 unintentional side effects.
 
-
 ##### Printing in AsyncHooks callbacks
 
 Because printing to the console is an asynchronous operation, `console.log()`
@@ -257,7 +256,6 @@ the new resource to initialize and that caused `init` to call. This is different
 from `async_hooks.executionAsyncId()` that only shows *when* a resource was
 created, while `triggerAsyncId` shows *why* a resource was created.
 
-
 The following is a simple demonstration of `triggerAsyncId`:
 
 ```js
@@ -395,7 +393,6 @@ API the user's callback is placed in a `process.nextTick()`.
 The graph only shows *when* a resource was created, not *why*, so to track
 the *why* use `triggerAsyncId`.
 
-
 ##### before(asyncId)
 
 * `asyncId` {number}
@@ -413,7 +410,6 @@ asynchronous resources like a TCP server will typically call the `before`
 callback multiple times, while other operations like `fs.open()` will call
 it only once.
 
-
 ##### after(asyncId)
 
 * `asyncId` {number}
@@ -424,7 +420,6 @@ If an uncaught exception occurs during execution of the callback, then `after`
 will run *after* the `'uncaughtException'` event is emitted or a `domain`'s
 handler runs.
 
-
 ##### destroy(asyncId)
 
 * `asyncId` {number}

doc/api/child_process.md

@@ -456,7 +456,6 @@ ls.on('close', (code) => {
 });
 ```
 
-
 Example: A very elaborate way to run `ps ax | grep ssh`
 
 ```js
@@ -494,7 +493,6 @@ grep.on('close', (code) => {
 });
 ```
 
-
 Example of checking for failed `spawn`:
 
 ```js