Repository: google/go-safeweb (go)

Issue:
Mismatch between the directory name and package name of the Fetch Metadata plugin
Currently it has to be imported like this:

```
import fetchmetadata "github.com/google/go-safeweb/safehttp/plugins/fetch_metadata"
```

Pull request description:
Remove "_" from fetch_metadata to make imports nicer.
Fixes #232.

Patch:
diff --git a/examples/echo/security/web/web.go b/examples/echo/security/web/web.go
index ebcc6f3..4d51b4f 100644
--- a/examples/echo/security/web/web.go
+++ b/examples/echo/security/web/web.go
@@ -26,7 +26,7 @@ import (
 	"github.com/google/go-safeweb/safehttp/plugins/coop"
 	"github.com/google/go-safeweb/safehttp/plugins/cors"
 	"github.com/google/go-safeweb/safehttp/plugins/csp"
-	fetchmetadata "github.com/google/go-safeweb/safehttp/plugins/fetch_metadata"
+	"github.com/google/go-safeweb/safehttp/plugins/fetchmetadata"
 	"github.com/google/go-safeweb/safehttp/plugins/hostcheck"
 	"github.com/google/go-safeweb/safehttp/plugins/hsts"
 	"github.com/google/go-safeweb/safehttp/plugins/staticheaders"


Test patch:
diff --git a/safehttp/plugins/fetch_metadata/fetch_metadata.go b/safehttp/plugins/fetchmetadata/fetchmetadata.go
similarity index 100%
rename from safehttp/plugins/fetch_metadata/fetch_metadata.go
rename to safehttp/plugins/fetchmetadata/fetchmetadata.go
diff --git a/safehttp/plugins/fetch_metadata/fetch_metadata_test.go b/safehttp/plugins/fetchmetadata/fetchmetadata_test.go
similarity index 99%
rename from safehttp/plugins/fetch_metadata/fetch_metadata_test.go
rename to safehttp/plugins/fetchmetadata/fetchmetadata_test.go
index eba7eb6..33d9358 100644
--- a/safehttp/plugins/fetch_metadata/fetch_metadata_test.go
+++ b/safehttp/plugins/fetchmetadata/fetchmetadata_test.go
@@ -19,7 +19,7 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-safeweb/safehttp"
-	"github.com/google/go-safeweb/safehttp/plugins/fetch_metadata"
+	"github.com/google/go-safeweb/safehttp/plugins/fetchmetadata"
 	"github.com/google/go-safeweb/safehttp/safehttptest"
 )