Add .webmanifest to extension map (#29)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e82ae09..d58625e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 # 1.0.3
 
+* Add application/manifest+json lookup by extension.
 * Add application/toml mimeType lookup by extension.
 * Add audio/aac mimeType lookup by header bytes.
 * Add audio/mpeg mimeType lookup by header bytes.
diff --git a/lib/src/default_extension_map.dart b/lib/src/default_extension_map.dart
index 64f4074..e66733f 100644
--- a/lib/src/default_extension_map.dart
+++ b/lib/src/default_extension_map.dart
@@ -898,6 +898,8 @@
   'wdp': 'image/vnd.ms-photo',
   'weba': 'audio/webm',
   'webm': 'video/webm',
+  // Source: https://w3c.github.io/manifest/#media-type-registration
+  'webmanifest': 'application/manifest+json',
   'webp': 'image/webp',
   'wg': 'application/vnd.pmi.widget',
   'wgt': 'application/widget',