better icon

src/vs/editor/contrib/review/comment.svg

-<svg xmlns="http://www.w3.org/2000/svg" x="0px" y="0px" viewBox="0 0 15 15" style="enable-background:new 0 0 15 15;">
-<line style="fill:none;stroke:#C5C5C5;stroke-miterlimit:10" x1="10" y1="7.5" x2="5" y2="7.5"/>
-<line style="fill:none;stroke:#C5C5C5;stroke-miterlimit:10" x1="7.5" y1="5" x2="7.5" y2="10"/>
-</svg>
\ No newline at end of file
+<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
+	 viewBox="0 0 16 16" style="enable-background:new 0 0 16 16;" xml:space="preserve">
+<path fill="#C5C5C5" class="st0" d="M13.3,2H2.7C2.2,2,1.8,2.4,1.8,2.9V10c0,0.4,0.4,0.9,0.9,0.9h1.8V14l3.1-3.1h5.8c0.4,0,0.9-0.4,0.9-0.9V2.9
+	C14.2,2.4,13.9,2,13.3,2z M9.2,9.7C9,9.7,8.9,9.6,8.9,9.6s0-0.5,0-1C8.9,8.2,8.8,8,8.6,8c0.8-0.1,1.6-0.4,1.6-1.8
+	c0-0.4-0.2-0.7-0.4-1c0-0.1,0.2-0.4,0-1c0,0-0.3-0.1-1,0.4C8.6,4.6,8.3,4.5,8,4.5c-0.3,0-0.6,0-0.9,0.1c-0.7-0.4-1-0.3-1-0.3
+	C6,4.8,6,5.2,6.1,5.3C5.9,5.5,5.7,5.8,5.7,6.2c0,1.3,0.8,1.7,1.6,1.8c0,0.1-0.1,0.2-0.2,0.4c-0.2,0.1-0.7,0.3-1-0.3
+	c0,0-0.2-0.4-0.5-0.4c0,0-0.4,0,0,0.2C5.6,8,5.9,8,6,8.5c0,0,0.2,0.7,1.2,0.4c0,0.3,0,0.5,0,0.6c0,0.1-0.1,0.2-0.3,0.2
+	C5.4,9.3,4.4,8,4.4,6.4c0-2,1.6-3.6,3.6-3.6s3.6,1.6,3.6,3.6C11.6,8,10.6,9.3,9.2,9.7z"/>
+</svg>

src/vs/editor/contrib/review/review.css

@@ -6,6 +6,8 @@
 .monaco-editor .margin-view-overlays .review {
 	background-image: url('comment.svg');
 	cursor: pointer;
+	background-repeat:no-repeat;
+	background-position: center center;
 }
 
 .monaco-editor .review-widget {