fix!: ensure consistency on grammar

Closes #56
~~~

doc/esqueleto.txt

@@ -42,7 +42,7 @@ To setup |esqueleto|, tow things must be done:
 First, |esqueleto| setup in the `init.lua` file is as follows: >
     require('esqueleto').setup({
           -- Default templates directory
-          directories = { '~/.config/nvim/skeleton/' },
+          directories = { '~/.config/nvim/skeletons/' },
 
           -- Patterns to detect for template insetion (empty by default,
           -- adding as an example)
@@ -75,7 +75,7 @@ steps:
 
 Based in the example seen above, the tree structure of our template directory
 should be: >
-    ~/.config/nvim/skeleton/
+    ~/.config/nvim/skeletons/
     ├── LICENSE
     ├── README.md
     └── python

lua/esqueleto/config.lua

@@ -4,7 +4,7 @@ local M = {}
 
 M.default_config = {
   autouse = true,
-  directories = { vim.fn.stdpath("config") .. "/skeleton" },
+  directories = { vim.fn.stdpath("config") .. "/skeletons" },
   patterns = function(dir) return vim.fn.readdir(dir) end,
   wildcards = {
     expand = true,