Fix find recursion in examples discovery (#129)

The find command that discovers example directories recurses into
subdirectories. Adding \`-maxdepth 0\` prevents this. Without the fix,
any example with a subdirectory would be treated as a separate example,
breaking the build. Discovered in ponylang/hobby.

Author: SeanTAllen

Makefile

@@ -40,7 +40,7 @@ endif
 PONYC := $(PONYC) $(SSL)
 
 SOURCE_FILES := $(shell find $(SRC_DIR) -name *.pony)
-EXAMPLES := $(notdir $(shell find $(EXAMPLES_DIR)/* -type d))
+EXAMPLES := $(notdir $(shell find $(EXAMPLES_DIR)/* -maxdepth 0 -type d))
 EXAMPLES_SOURCE_FILES := $(shell find $(EXAMPLES_DIR) -name *.pony)
 EXAMPLES_BINARIES := $(addprefix $(BUILD_DIR)/,$(EXAMPLES))