Help text typo SYNOPSYS => SYNOPSIS (#74)

diff --git a/main.cpp b/main.cpp
index d0c00dc..1746f9b 100644
--- a/main.cpp
+++ b/main.cpp
@@ -563,7 +563,7 @@
             }
         }
         if (!no_synopsis) {
-            section_header("SYNOPSYS");
+            section_header("SYNOPSIS");
             for (auto &s : synopsis) {
                 fos.first_column(tab);
                 fos.hanging_indent((int)tool_name.length() + tab);