update logo

README.md

-![gstlal](https://git.ligo.org/lscsoft/gstlal/raw/master/doc/source/_static/gstlal_small.png "gstlal")
+![gstlal](https://git.ligo.org/lscsoft/gstlal/raw/master/doc/source/_static/gstlal.png "gstlal")
 
 GStreamer elements for gravitational-wave data analysis
 ==================================================================

doc/source/_static/css/my_theme.css

 /* Uses skorch docs theme from https://skorch.readthedocs.io */
 
 .wy-side-nav-search {
-    background-color: #fcfcfc;
+    background-color: #ffffff;
 
 }
 
@@ -16,7 +16,7 @@
 /* Adds logo in header for mobile */
 
 .wy-nav-top {
-    background-color: #fcfcfc;
+    background-color: #ffffff;
     background-image: url('../logo.svg');
     background-repeat: no-repeat;
     background-position: bottom;