Updated font we use to Nunito

apps/explorer_web/assets/css/theme/_fonts.scss

@@ -1,2 +1,2 @@
-@import url('https://fonts.googleapis.com/css?family=Roboto+Mono');
+@import url('https://fonts.googleapis.com/css?family=Nunito');
 @import url('https://fonts.googleapis.com/css?family=Roboto');

apps/explorer_web/assets/css/theme/_poa_variables.scss

@@ -231,8 +231,8 @@ $transition-collapse:         height .35s ease !default;
 // Font, line-height, and color for body text, headings, and more.
 
 // stylelint-disable value-keyword-case
-$font-family-sans-serif:      Roboto, "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol" !default;
-$font-family-monospace:       "Roboto Mono", SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace !default;
+$font-family-sans-serif:      Nunito, "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol" !default;
+$font-family-monospace:       SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace !default;
 $font-family-base:            $font-family-sans-serif !default;
 // stylelint-enable value-keyword-case