Map props patch (#55)

* remove string for props in function

* Update mapblock.h to add props string. 

* Update library.properties

Author: brentru

library.properties

@@ -1,5 +1,5 @@
 name=Adafruit IO Arduino
-version=2.7.12
+version=2.7.13    
 author=Adafruit
 maintainer=Adafruit <adafruitio@adafruit.com>
 sentence=Arduino library to access Adafruit IO.

src/blocks/MapBlock.cpp

@@ -27,11 +27,11 @@ String MapBlock::properties()
         tile = "contrast";
     }
 
-    String props = "{\"historyHours\":\"";
+    props = "{\"historyHours\":\"";
     props += historyHours;
     props += "\",\"tile\":\"";
     props += tile;
     props += "\"}";
 
     return props;
-}
+}

src/blocks/MapBlock.h

@@ -19,7 +19,8 @@ class MapBlock : public AdafruitIO_Block {
   public:
     MapBlock(AdafruitIO_Dashboard *d, AdafruitIO_Feed *f);
     ~MapBlock();
-
+  
+    String props;
     int historyHours;
     const char *tile;