Add Cairo as required package

In reference to issue #5
diff --git a/.Rproj.user/441ADA46/sources/prop/60EAAA4E b/.Rproj.user/441ADA46/sources/prop/60EAAA4E
index 9960a89..c8a6372 100644
--- a/.Rproj.user/441ADA46/sources/prop/60EAAA4E
+++ b/.Rproj.user/441ADA46/sources/prop/60EAAA4E
@@ -1,4 +1,4 @@
 {
-    "cursorPosition" : "4,131",
-    "scrollLine" : "0"
+    "cursorPosition" : "32,0",
+    "scrollLine" : "26"
 }
\ No newline at end of file
diff --git a/.Rproj.user/441ADA46/sources/prop/AE6C9F23 b/.Rproj.user/441ADA46/sources/prop/AE6C9F23
index 7a73a41..7d1ed6b 100644
--- a/.Rproj.user/441ADA46/sources/prop/AE6C9F23
+++ b/.Rproj.user/441ADA46/sources/prop/AE6C9F23
@@ -1,2 +1,4 @@
 {
+    "cursorPosition" : "15,14",
+    "scrollLine" : "0"
 }
\ No newline at end of file
diff --git a/.Rproj.user/441ADA46/sources/prop/B68389EB b/.Rproj.user/441ADA46/sources/prop/B68389EB
index 6519c24..1c34024 100644
--- a/.Rproj.user/441ADA46/sources/prop/B68389EB
+++ b/.Rproj.user/441ADA46/sources/prop/B68389EB
@@ -1,4 +1,4 @@
 {
-    "cursorPosition" : "41,0",
-    "scrollLine" : "0"
+    "cursorPosition" : "83,65",
+    "scrollLine" : "76"
 }
\ No newline at end of file