doc: fix default sourceMap value (#232)

Author: kaisermann

docs/preprocessing.md

@@ -71,7 +71,7 @@ The following options can be passed to the preprocessor. None are required:
 | `aliases`       | `null`                                                   | A list of tuples `[alias: string, language: string]` that correlates an `alias` to a `language`<br><br>i.e `['cst', 'customLanguage']` means<br>`<... src="./file.cst">`<br>`<... lang="cst">`<br>`<... type="text/customLanguage">`<br>`<... type="application/customLanguage">`<br>are treated as `customLanguage`. |
 | preserve        | `[]`                                                     | A `string` list of languages/aliases that shouldn't pass through the preprocessor. (i.e `ld+json`)                                                                                                                                                                                                                    |
 | `defaults`      | `{ markup: 'html', script: 'javascript', style: 'css' }` | An `object` that defines the default languages of your components.<br><br>i.e: `{ script: 'typescript' }` makes TypeScript the default language, removing the need of adding `lang="ts"` to `script` tags.                                                                                                            |
-| `sourceMap`     | `true`                                                   | If `true`, `svelte-preprocess` generates sourcemap for every language that supports it.                                                                                                                                                                                                                               |
+| `sourceMap`     | `false`                                                   | If `true`, `svelte-preprocess` generates sourcemap for every language that supports it.                                                                                                                                                                                                                               |
 
 ##### Configuring preprocessors