Social: update Facebook's color code (#13681)

Facebook's Logo now uses a different shade of blue, as per the brand guidelines:
https://en.facebookbrand.com/assets/f-logo/

Author: jeherve

_inc/client/scss/variables/_colors.scss

@@ -69,7 +69,7 @@ $sidebar-selected-color:   $gray;
 $dashboard-number-border: #CBD7E1;
 
 //Social media colors
-$color-facebook:    #39579a;
+$color-facebook:    #1877F2;
 $color-twitter:     #55ACEE;
 $color-gplus:       #df4a32;
 $color-tumblr:      #35465c;

modules/calypsoify/_colors.scss

@@ -71,7 +71,7 @@ $sidebar-selected-color:   $gray-text-min;
 
 
 //Social media colors
-$color-facebook: #39579a;
+$color-facebook: #1877F2;
 $color-twitter: #55ACEE;
 $color-gplus: #df4a32;
 $color-tumblr: #35465c;

modules/sharedaddy/sharing.css

@@ -599,7 +599,7 @@ body .sd-social-icon .sd-content li.share-custom a span {
 }
 
 .sd-social-icon .sd-content ul li[class*='share-'].share-facebook a.sd-button {
-	background: #3b5998;
+	background: #1877F2;
 	color: #fff !important;
 }