Fix comments about filenames in some programs
diff --git a/programs/pkey/pk_verify.c b/programs/pkey/pk_verify.c
index 8ab5c93..fa3c0e0 100644
--- a/programs/pkey/pk_verify.c
+++ b/programs/pkey/pk_verify.c
@@ -86,7 +86,7 @@
     }
 
     /*
-     * Extract the signature from the text file
+     * Extract the signature from the file
      */
     ret = 1;
     mbedtls_snprintf( filename, sizeof(filename), "%s.sig", argv[2] );